Depressive symptoms are among the most common neuropsychiatric manifestations of general medical illness, and the diagnosis of Depressive disorder due to another medical condition identifies the subset in which a specific medical condition is judged to be the direct pathophysiologic cause of the mood disturbance. DSM-5-TR places the diagnosis within the Depressive Disorders chapter and requires that the depressive presentation be the direct physiological consequence of the medical condition rather than a psychological reaction to being ill. The distinction matters clinically because treatment of the underlying condition — hypothyroidism, stroke, Cushing syndrome, multiple sclerosis, Parkinson disease, interferon therapy — often improves or resolves the depressive syndrome, while depression-specific treatment alone may underperform. Stroke, Parkinson disease, hypothyroidism, and several autoimmune and endocrine disorders are the prototypical causes that boards and consult services expect trainees to recognize on sight. The bottom line: when depression presents atypically, at an unusual age, or alongside a known systemic illness, the workup belongs as much in the medical chart as in the psychiatric formulation.

Depression is overrepresented across nearly every category of chronic medical illness, but only a fraction of those presentations meet criteria for depressive disorder due to another medical condition rather than a primary mood disorder or adjustment reaction. Population-level estimates vary widely by condition and ascertainment method.

Prevalence by condition

• Post-stroke depression occurs in roughly one-third of stroke survivors at some point in the first year, with point prevalence around 30 to 35 percent.^1-2
• Parkinson disease carries a depression prevalence of approximately 35 to 40 percent across the disease course, with clinically significant depression in about 17 percent at any time.³
• Major depression complicates multiple sclerosis in roughly a quarter of patients, with lifetime prevalence reaching 50 percent in some cohorts.⁴
• Hypothyroidism (overt and subclinical) is associated with depressive symptoms in 30 to 60 percent of affected patients in clinical samples.⁵
• Cushing syndrome produces depressive symptoms in over half of cases at presentation.⁶
• Interferon-alfa therapy for chronic hepatitis C induced clinically significant depression in 20 to 40 percent of treated patients in pre-direct-acting-antiviral era trials.⁷

Demographic and risk patterns

• Age of onset tracks the underlying medical condition rather than the bimodal age distribution of primary major depressive disorder.⁸
• Female predominance seen in primary Major depressive disorder is attenuated or absent in several medical-illness-associated depressions, including post-stroke depression.¹
• Personal or family history of primary mood disorder increases vulnerability to depression in the setting of a new medical illness but does not by itself make a presentation primary.⁸
• Comorbid anxiety disorders, cognitive impairment, and substance use are common and worsen prognosis.^3-4
• Suicide risk is elevated in several causal conditions, particularly Huntington disease, multiple sclerosis, and early post-stroke periods.^4,9

The shared feature across causal conditions is direct disruption of the neural systems that subserve mood, motivation, and reward — whether by focal lesion, neuroendocrine dysregulation, neuroinflammation, or pharmacologic effect of a treatment for the underlying disease. The mechanism is condition-specific.

Mechanistic categories

• Focal central nervous system lesions disrupt frontal-subcortical mood circuits. Left dorsolateral prefrontal and left basal ganglia strokes have been most consistently associated with post-stroke depression, although meta-analyses have moderated the strength of the lesion-location hypothesis.^2,10
• Neurodegenerative depletion of monoaminergic nuclei contributes in Parkinson disease, where loss of dopaminergic, noradrenergic (locus coeruleus), and serotonergic (dorsal raphe) neurons predates and parallels mood symptoms.³
• Demyelinating and inflammatory injury in multiple sclerosis affects frontal and temporal regions; cytokine-mediated neuroinflammation contributes independently of lesion burden.⁴
• Endocrine disruption operates through hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axis effects. Hypercortisolism (Cushing), hypothyroidism, hyperparathyroidism, and hypogonadism are the classical examples.^5-6
• Cytokine-induced sickness behavior — fatigue, anhedonia, psychomotor slowing — is the proposed mechanism for interferon-, IL-2-, and chronic-inflammation-associated depression, mediated in part by indoleamine 2,3-dioxygenase activation and tryptophan diversion to the kynurenine pathway.^7,11
• Direct pharmacologic effect of prescribed medications produces a syndrome that DSM-5-TR classifies separately as substance/medication-induced depressive disorder rather than depression due to another medical condition, but the mechanisms overlap.¹²

Conditions with the strongest causal evidence

• Neurologic: stroke, Parkinson disease, Huntington disease, multiple sclerosis, traumatic brain injury, epilepsy (particularly temporal lobe), dementias.^2-4,9,13
• Endocrine: hypothyroidism, hyperthyroidism, Cushing syndrome, Addison disease, hyperparathyroidism, hypogonadism.^5-6
• Metabolic and nutritional: vitamin B12 deficiency, folate deficiency, hypercalcemia, hyponatremia.¹³
• Autoimmune and inflammatory: systemic lupus erythematosus, autoimmune encephalitis (notably anti-NMDA receptor and limbic encephalitides).¹⁴
• Infectious: HIV, neurosyphilis, hepatitis C, post-COVID-19 syndromes.^7,15
• Oncologic: pancreatic, lung, and CNS malignancies; paraneoplastic syndromes.¹³

DSM-5-TR specifies that the clinician identify both a depressive syndrome and a specific medical condition judged on physiologic grounds to be its direct cause. The diagnosis is not made when the depressive symptoms are better explained by another mental disorder, occur exclusively during delirium, or arise as a psychological reaction to having an illness — the latter is adjustment disorder with depressed mood.¹⁶

DSM-5-TR criteria summarized

• A prominent and persistent period of depressed mood or markedly diminished interest or pleasure in nearly all activities dominates the clinical picture.¹⁶
• History, examination, or laboratory findings establish that the disturbance is the direct pathophysiologic consequence of another medical condition.¹⁶
• The disturbance is not better explained by another mental disorder such as adjustment disorder with depressed mood, where the stressor is the medical condition itself.¹⁶
• The disturbance does not occur exclusively during the course of a delirium.¹⁶
• The disturbance causes clinically significant distress or impairment in social, occupational, or other important areas of functioning.¹⁶

Specifiers

• With depressive features: full criteria for a major depressive episode are not met.¹⁶
• With major depressive-like episode: full criteria (except criterion C) for a major depressive episode are met.¹⁶
• With mixed features: depressive symptoms accompanied by manic or hypomanic features that do not predominate.¹⁶

Coding and naming convention

• The diagnostic name should explicitly include the causal medical condition, for example "depressive disorder due to hypothyroidism, with major depressive-like episode."¹⁶
• The associated medical condition is coded first, followed by the depressive disorder due to the medical condition.¹⁶

ICD-11 differences

• ICD-11 captures these presentations under "secondary mood syndrome," with subtypes for depressive, manic, mixed, and other specifiers, organized within the chapter on mental, behavioural and neurodevelopmental disorders.¹⁷
• ICD-11 explicitly separates secondary psychiatric syndromes from primary mood disorders to support causal coding linked to the underlying medical condition.¹⁷

The phenotype overlaps substantially with primary major depressive disorder, but clues to a secondary etiology emerge from the temporal relationship to the medical condition, the prominence of somatic and cognitive features, and atypical demographics. A high index of suspicion is warranted whenever depression presents at an unusual age or in a patient with a known systemic illness.^8,13

Symptom profile

• Mood symptoms include depressed mood, anhedonia, hopelessness, and tearfulness, often with prominent apathy that can dominate the picture in Parkinson disease, frontal-lobe stroke, and dementias.^3,18
• Somatic features — fatigue, psychomotor slowing, sleep disturbance, appetite change — may be difficult to distinguish from manifestations of the underlying medical condition itself.¹³
• Cognitive complaints, including impaired concentration, slowed processing, and executive dysfunction, are common and may resemble dementia (depressive pseudodementia).¹⁸
• Irritability, anxiety, and emotional lability are frequent, particularly in stroke, traumatic brain injury, and multiple sclerosis.^2,4
• Suicidal ideation is reported across causal conditions and should be assessed at every visit; risk is particularly elevated in Huntington disease and early multiple sclerosis.^4,9

Prototypical presentations

• Post-stroke depression: emerges within the first three to six months after stroke; often features apathy, emotional lability, and pseudobulbar affect.²
• Parkinson disease depression: anhedonia and apathy with relatively preserved guilt and self-blame; may precede motor symptoms by years.³
• Hypothyroid depression: fatigue, cognitive slowing, weight gain, and cold intolerance; reverses with thyroid replacement in most patients.⁵
• Cushing depression: irritability, anxiety, and mood lability more than classical melancholia; resolves with normalization of cortisol.⁶
• Interferon-alfa-associated depression: emerges within weeks of initiation, with prominent neurovegetative and cognitive symptoms.⁷

Red flags for a secondary etiology

• First episode of depression after age 50 without prior psychiatric history.^8,13
• Atypical or treatment-resistant course in a patient with known systemic illness.¹³
• Prominent cognitive impairment out of proportion to mood symptoms.¹⁸
• Focal neurologic findings, abnormal vital signs, or unexplained constitutional symptoms.¹³
• Symptom onset temporally linked to initiation of a new medication or relapse of a chronic disease.¹²

The central diagnostic question is causal: does the medical condition produce the depression through a physiologic mechanism, or is the depression a primary mood disorder that happens to co-occur, a psychological reaction to illness, or an effect of treatment? The DSM-5-TR demands evidence of direct physiologic causation, which is a higher bar than temporal association.¹⁶

Key differentials

• Major depressive disorder: primary mood disorder with no demonstrable medical cause; family and personal psychiatric history, prior episodes, and absence of a temporally and mechanistically linked medical condition support this diagnosis.¹⁶
• Adjustment disorder with depressed mood: depressive symptoms arise as a psychological reaction to the stress of having a medical illness rather than as a direct pathophysiologic consequence; severity does not meet full criteria for a major depressive episode and the link is psychosocial rather than physiologic.¹⁶
• Substance/medication-induced depressive disorder: depression caused by pharmacologic agents (corticosteroids, interferon-alfa, varenicline, reserpine, beta-blockers in susceptible patients, hormonal therapies) or substances of abuse (alcohol, sedative withdrawal, stimulant withdrawal).^12,16
• Bipolar depression with comorbid medical illness: requires a personal history of mania or hypomania; the medical condition may exacerbate but did not cause the underlying mood disorder.¹⁶
• Delirium with depressive features: fluctuating attention, acute onset, and altered consciousness distinguish delirium; depressive symptoms occurring exclusively during delirium are not separately diagnosed.¹⁶
• Major or mild neurocognitive disorder: cognitive impairment is the dominant feature; depressive features may co-occur and merit a co-diagnosis if criteria are met.¹⁸
• Demoralization syndrome: hopelessness and existential distress in the context of chronic illness, without the full neurovegetative profile of depression; an important construct in palliative-care psychiatry.¹⁹
• Hypoactive delirium and fatigue from the underlying disease: can mimic depressive psychomotor retardation but lack persistent depressed mood or anhedonia.¹³

Medical mimics to screen actively

• Endocrine: hypothyroidism, hyperthyroidism, Cushing syndrome, Addison disease, hyperparathyroidism, hypogonadism, diabetes.^5-6
• Neurologic: stroke, Parkinson disease, multiple sclerosis, Huntington disease, traumatic brain injury, epilepsy, normal pressure hydrocephalus, dementia.^2-4,9,18
• Metabolic and nutritional: B12 or folate deficiency, hyponatremia, hypercalcemia, uremia, hepatic encephalopathy.¹³
• Autoimmune: systemic lupus erythematosus, autoimmune encephalitis, paraneoplastic syndromes.¹⁴
• Infectious: HIV, syphilis, hepatitis C, Lyme disease, post-COVID-19 syndromes.^7,15
• Oncologic: pancreatic cancer, lung cancer (especially small cell with paraneoplastic features), CNS tumors.¹³
• Sleep disorders: obstructive sleep apnea is a frequent reversible contributor to treatment-resistant depressive symptoms.²⁰

Evaluation requires a synthesis of psychiatric interview, careful medical history, focused physical and neurologic examination, and targeted laboratory testing. The standard for diagnosis is that the medical condition is plausibly causal on physiologic grounds, and assessment is structured to test that hypothesis.¹⁶

Interview essentials

• Detailed temporal history of mood symptoms in relation to the medical condition, its treatments, and any flares.¹³
• Complete review of systems with attention to constitutional, neurologic, endocrine, and cardiopulmonary symptoms.¹³
• Full medication reconciliation including over-the-counter agents, supplements, hormonal therapies, and recent corticosteroid exposure.¹²
• Substance use history including alcohol, cannabis, stimulants, and prescription opioids.¹⁶
• Personal and family psychiatric history to gauge primary mood-disorder vulnerability.⁸
• Suicide and safety assessment at every encounter.⁹

Physical and neurologic examination

• Vital signs and general examination, including weight change, skin and hair findings (myxedema, hyperpigmentation, striae), and thyroid examination.^5-6
• Focused neurologic examination for focal deficits, parkinsonism, gait abnormality, and cerebellar signs.^2-3
• Cognitive screening with a validated instrument such as the Montreal Cognitive Assessment (MoCA) when cognitive features are prominent.¹⁸

Rating scales

• Patient Health Questionnaire-9 (PHQ-9) for severity tracking; remains valid in medical populations although somatic items may inflate scores.²¹
• Hamilton Depression Rating Scale (HAM-D) and Montgomery-Asberg Depression Rating Scale (MADRS) for research-grade assessment.²²
• Hospital Anxiety and Depression Scale (HADS) was developed specifically for medically ill patients and minimizes somatic item bias.²³
• Geriatric Depression Scale (GDS) for older adults with medical comorbidity.²⁴
• Cornell Scale for Depression in Dementia when the patient has significant cognitive impairment.²⁵

Laboratory and imaging workup

• Initial laboratory screen typically includes complete blood count, comprehensive metabolic panel, TSH (with free T4 if abnormal), vitamin B12, folate, and urinalysis.¹³
• Add HIV testing, syphilis serology, hepatitis serologies, and toxicology when indicated by history.¹³
• Endocrine workup with morning cortisol, dexamethasone suppression testing, or 24-hour urinary free cortisol when Cushing syndrome is suspected.⁶
• Neuroimaging (MRI preferred over CT) for new-onset depression after age 50, focal neurologic findings, or atypical features.¹³
• EEG when seizures, episodic symptoms, or autoimmune encephalitis are considered.¹⁴
• Lumbar puncture and autoimmune encephalitis antibody panels in suspected limbic or anti-NMDA receptor encephalitis.¹⁴

Management proceeds along two parallel tracks: optimize treatment of the underlying medical condition, and treat the depressive syndrome directly when it persists, is severe, or carries safety risk. In many cases — hypothyroidism, Cushing syndrome, and B12 deficiency are the classical examples — correction of the underlying disorder substantially or fully resolves the depression.^5-6,13 Once the diagnosis is settled, the harder question is what to do about the depression when condition-directed treatment alone is insufficient.

General principles

• Treat the underlying medical condition first or in parallel; depression-specific therapy alone often underperforms when the causal pathophysiology is untreated.¹³
• Review and minimize potentially depressogenic medications where clinically feasible.¹²
• Address sleep, pain, nutritional status, and physical deconditioning, all of which act as modifiable amplifiers.¹³
• Engage caregivers and the primary medical team early; coordination is the single most important factor in consult-liaison outcomes.²⁶

Pharmacotherapy

• Evidence suggests SSRIs are the preferred first-line agents in most causal conditions because of favorable tolerability and modest interaction profiles; SSRIs such as sertraline, escitalopram, and citalopram have the largest evidence base in medical populations.^26-27
• Strong evidence supports SSRIs (particularly fluoxetine and nortriptyline in older trials, and citalopram and escitalopram more recently) for post-stroke depression, with meta-analyses showing modest but consistent benefit over placebo.²⁸
• Evidence suggests SSRIs and SNRIs improve depressive symptoms in Parkinson disease, with tricyclics (notably nortriptyline and desipramine) also effective; bupropion and pramipexole are reasonable alternatives that may target apathy and motor symptoms simultaneously.²⁹
• For multiple sclerosis-associated depression, limited evidence suggests SSRIs are commonly recommended, although the evidence base is smaller and largely extrapolated from primary depression trials.⁴
• For depression with prominent fatigue or pain in medical illness, SNRIs (duloxetine, venlafaxine) and bupropion are commonly considered.²⁷
• Mirtazapine is useful when insomnia, weight loss, or nausea predominate, particularly in oncology and palliative-care settings.²⁷
• Avoid tricyclics in patients with significant cardiac conduction disease, urinary retention, narrow-angle glaucoma, or postural hypotension.²⁷
• Methylphenidate and other psychostimulants have a niche role in medically ill patients with prominent apathy or in palliative care where rapid onset is desirable; evidence is low quality but clinically established.³⁰

Psychotherapy

• Evidence suggests cognitive behavioral therapy reduces depressive symptoms in chronic medical illness including post-stroke depression, multiple sclerosis, and cancer.³¹
• Limited evidence suggests behavioral activation, problem-solving therapy, and interpersonal psychotherapy are effective adjuncts, particularly when accessibility favors brief structured therapies.³¹
• Supportive psychotherapy and meaning-centered approaches are commonly recommended for patients with advanced or terminal illness, where existential distress complicates the clinical picture.¹⁹
• Caregiver-inclusive approaches are commonly recommended in neurodegenerative disease where caregiver burden is a major source of relapse.³

Neuromodulation

• Evidence suggests electroconvulsive therapy is effective and often rapidly so for severe, refractory, psychotic, or catatonic depression in medically ill patients, including those with Parkinson disease where it may also improve motor symptoms.³²
• Repetitive transcranial magnetic stimulation has growing evidence in primary depression and is considered when pharmacotherapy is poorly tolerated; condition-specific evidence in secondary depression is more limited.³²
• Vagus nerve stimulation and deep brain stimulation have a limited role and are reserved for highly refractory cases at specialized centers.³³

Adjunctive

• Aerobic exercise improves depressive symptoms in multiple sclerosis, Parkinson disease, post-stroke recovery, and cancer survivorship; limited evidence but consistent benefit.³⁴
• Bright light therapy is commonly recommended for seasonal patterns and for Parkinson disease depression with sleep-wake disturbance.²⁹
• Treatment of comorbid obstructive sleep apnea with continuous positive airway pressure improves residual depressive symptoms in a meaningful subset of patients.²⁰
• Nutritional repletion (B12, folate, vitamin D) when deficient; some experts recommend folate or L-methylfolate augmentation in partial responders, though high-quality evidence is lacking.¹³

Treating depression in medically ill patients exposes them to interaction-prone polypharmacy and to adverse effects that are amplified by the underlying illness. The evidence base, although growing, is condition-specific and dominated by small to moderate-sized trials with heterogeneous outcomes.

Common adverse effects

• SSRIs and SNRIs commonly cause gastrointestinal upset, sexual dysfunction, sleep disturbance, and hyponatremia, the latter particularly in older adults and patients on diuretics.^27,37
• SSRIs increase bleeding risk modestly, an effect of concern in patients on anticoagulants or with peptic ulcer disease.^27,37
• TCAs cause anticholinergic effects, orthostatic hypotension, sedation, weight gain, and conduction-system effects that can be intolerable in cardiac and neurologic disease.²⁷
• Bupropion lowers seizure threshold and is contraindicated in patients with active seizure disorder, eating disorders, or recent benzodiazepine or alcohol withdrawal.²⁷
• Mirtazapine causes sedation and weight gain; these can be desirable or limiting depending on the clinical setting.²⁷
• Psychostimulants risk tachycardia, hypertension, anxiety, and appetite suppression.³⁰

Serious or rare adverse effects

• Serotonin syndrome is a clinically relevant risk when serotonergic agents are combined, especially with linezolid, methylene blue, tramadol, or other antidepressants.²⁷
• QT prolongation is dose-dependent with citalopram and to a lesser extent escitalopram; relevant in patients with cardiac disease or on QT-prolonging agents.³⁵
• ECT carries anesthetic risk, transient cognitive effects, and rare cardiovascular complications; the risk-benefit calculus shifts favorably in severe medication-refractory or psychotic depression.³²

Monitoring and discontinuation

• Sodium monitoring is reasonable in older adults starting SSRIs/SNRIs, particularly those on thiazides.³⁶
• ECG monitoring is appropriate when initiating citalopram or TCAs in patients with cardiac risk factors.³⁵
• Antidepressant discontinuation syndrome is more common with short-half-life agents (paroxetine, venlafaxine) and warrants tapered withdrawal.²⁷
• Risk of antidepressant-emergent mania exists in patients with undiagnosed bipolar disorder; reassess if hypomanic or manic features emerge.²⁷

Limitations of the evidence base

• Most condition-specific antidepressant trials are small, short, and heterogeneous in inclusion criteria; meta-analyses report effects ranging from modest to nonsignificant depending on inclusion thresholds.^28-29
• Outcome measures rely on symptom scales designed for primary depression and may inflate or deflate scores due to somatic-item overlap with the underlying medical condition.²¹
• Few trials directly compare antidepressant classes or compare antidepressants against optimized condition-directed therapy alone.²⁸
• Long-term outcome data, including effects on disability and mortality, are limited outside post-stroke and cancer populations.^2,38

Patient-specific factors — age, pregnancy, comorbid disease, polypharmacy — modify both the differential and the safe treatment options. Geriatric and perinatal contexts are the most commonly tested on examinations.

Pediatric

• Secondary depression in children is rare and most commonly associated with epilepsy, traumatic brain injury, endocrinopathies, and chemotherapy or immunotherapy exposures.¹³
• Differential includes pediatric autoimmune neuropsychiatric disorders, anti-NMDA receptor encephalitis, and pediatric multiple sclerosis.¹⁴
• Treatment follows pediatric mood-disorder principles with attention to FDA black-box warning on antidepressants and suicidality in those under 25.²⁷

Geriatric

• New-onset depression after 50 carries a substantially elevated pretest probability of a medical or neurologic cause and warrants targeted workup.^8,13
• Vascular depression — depression with white matter hyperintensities and executive dysfunction — is a clinically important variant in older adults.³⁸
• Start antidepressants at half the usual adult starting dose and titrate slowly; monitor sodium, falls, and cognitive effects.³⁶
• Avoid TCAs and strongly anticholinergic agents.³⁶

Perinatal

• Pregnancy-related medical conditions, including postpartum thyroiditis, Sheehan syndrome, and pregnancy-associated autoimmune flares, can cause secondary depression that may be misattributed to postpartum depression.³⁹
• Workup should include TSH at minimum in postpartum depression with atypical features.³⁹
• Antidepressant selection in pregnancy and lactation follows standard perinatal principles; sertraline has the most reassuring lactation data.⁴⁰

Comorbid medical illness

• Cardiac disease: SSRIs (sertraline, escitalopram) are preferred; the SADHART trial supports sertraline safety post-MI.⁴¹
• Renal and hepatic impairment: dose adjustment for most antidepressants; sertraline and citalopram require modest adjustments in hepatic impairment.²⁷
• Oncology: mirtazapine has favorable effects on appetite, sleep, and nausea; methylphenidate has rapid benefit for fatigue and depression at end of life.³⁰
• Epilepsy: SSRIs are generally considered safe at therapeutic doses; bupropion is relatively contraindicated.²⁷

Comorbid substance use

• Active alcohol or sedative use can mimic and worsen depression; reassess after a period of abstinence when possible.¹⁶
• Hepatitis C-related depression in patients with active or remote substance use requires careful interferon and direct-acting antiviral history; modern direct-acting antivirals carry markedly lower psychiatric burden than interferon-based regimens.⁷

Cultural considerations

• Somatic presentations of depression are more common in some cultural contexts and can overlap with medical-illness symptoms; this affects both diagnosis and rating-scale interpretation.⁴²

Outcome depends primarily on the trajectory of the underlying medical condition and on whether depression-specific treatment is delivered in addition to condition-directed care. Persistent depression independently worsens functional outcomes, healthcare utilization, and mortality.

Course patterns

• Reversible causes (hypothyroidism, B12 deficiency, hypercortisolism, interferon discontinuation) often produce resolution of depressive symptoms within weeks to months of correction.^5-7
• Progressive neurodegenerative causes (Parkinson disease, Huntington disease, dementias) have a chronic, often recurrent depressive course requiring long-term management.^3,9,18
• Stroke-related depression peaks at 3 to 6 months and frequently remits by one to two years, but a substantial minority remain chronic.²
• Multiple sclerosis-related depression often follows a relapsing course paralleling disease activity.⁴

Response and remission

• Antidepressant response rates in medically ill populations approximate 40 to 60 percent across conditions, broadly comparable to but somewhat lower than primary major depression.^28-29
• Treatment-resistant presentations are common when the underlying condition is undertreated or progressive.¹³

Mortality and functional impact

• Depression after myocardial infarction independently increases cardiac mortality.⁴¹
• Post-stroke depression worsens rehabilitation outcomes, increases mortality, and lengthens disability.²
• Depression in cancer is associated with poorer treatment adherence and shorter survival in several cohorts.³⁷
• Suicide risk is elevated across many causal conditions, with the highest relative risks reported in Huntington disease, multiple sclerosis, and the early post-diagnosis period of major medical illness.^4,9

Acute safety risks in this population include suicide, severe medical decompensation masquerading as depression, and catatonia or psychosis associated with the underlying condition. Threshold for hospitalization should reflect both psychiatric and medical risk.

Hospitalization criteria

• Active suicidal ideation with intent or plan, particularly in conditions with elevated baseline suicide risk.⁹
• Severe nutritional or self-care decline jeopardizing medical stability.¹³
• Suspected acute medical mimic requiring inpatient workup (e.g., new neurologic findings, suspected autoimmune encephalitis, electrolyte derangement, undiagnosed Cushing or Addison crisis).¹⁴
• Catatonic features or psychotic depression requiring inpatient stabilization and potential ECT.³²

Suicide risk markers

• Hopelessness, severe insomnia, prior attempts, recent loss, perceived burdensomeness, access to lethal means.⁹
• High-risk causal conditions: Huntington disease, multiple sclerosis (particularly within the first year of diagnosis), traumatic brain injury, post-stroke (early period), and chronic pain conditions.^4,9

Agitation management

• Identify and treat reversible contributors (pain, delirium, urinary retention, hypoxia) before reaching for antipsychotics.⁴³
• Verbal de-escalation and environmental modification are first-line; pharmacologic management follows standard agitation protocols.⁴³

Several debates shape current practice and are likely to evolve as evidence accumulates.

Open questions

• The lesion-location hypothesis for post-stroke depression has been moderated by larger meta-analyses; whether left frontal or basal ganglia lesions reliably predict depression remains debated.¹⁰
• Whether SSRIs improve functional recovery in post-stroke depression beyond their mood effects is contested; the FOCUS trial did not show benefit on functional outcomes for fluoxetine in unselected stroke survivors, and similar negative results emerged from the EFFECTS and AFFINITY trials.⁴⁴
• The relative contribution of disease-specific neurobiology versus a shared inflammatory or HPA-axis mechanism across causal conditions is unresolved.¹¹
• Optimal screening tools and cutoffs for depression in medically ill populations remain debated, given somatic-item overlap.^21,23
• The role of psilocybin, ketamine, and esketamine in depression secondary to medical illness is uncertain; published trials have largely excluded these populations.⁴⁵
• ICD-11's "secondary mood syndrome" framework differs from DSM-5-TR and may influence cross-jurisdictional coding and research comparability.¹⁷

• DSM-5-TR requires that the depressive disturbance be the direct physiologic consequence of a specified medical condition.¹⁶
• The diagnosis is not made when depressive symptoms occur exclusively during delirium.¹⁶
• Depression occurring as a psychological reaction to having a medical illness is adjustment disorder with depressed mood, not depression due to another medical condition.¹⁶
• Medication-induced depression (e.g., corticosteroids, interferon-alfa) is coded as substance/medication-induced depressive disorder, not under depression due to another medical condition.^12,16
• Post-stroke depression occurs in roughly one-third of stroke survivors, most commonly within the first three to six months.²
• Parkinson disease depression is characterized by prominent anhedonia and apathy and may precede motor symptoms.³
• Hypothyroidism, hyperthyroidism, Cushing syndrome, and Addison disease are classical endocrine causes of secondary depression.^5-6
• New-onset depression after age 50 warrants targeted medical workup including TSH, B12, and neuroimaging when indicated.^8,13
• Vascular depression is characterized by white matter hyperintensities and executive dysfunction in older adults.³⁸
• Sertraline is preferred for depression after myocardial infarction based on SADHART safety data.⁴¹
• Citalopram doses above 40 mg/day (20 mg in older adults) increase QT prolongation risk and should be avoided.³⁵
• ECT is effective and often rapidly so for severe or refractory depression in medically ill patients and may improve motor symptoms in Parkinson disease.³²
• Bupropion is relatively contraindicated in active seizure disorder and eating disorders.²⁷
• Autoimmune encephalitis can present with rapid-onset depression and cognitive change; missed diagnosis carries serious morbidity.¹⁴
• Suicide risk is elevated in Huntington disease, multiple sclerosis (particularly early after diagnosis), and the early post-stroke period.^4,9

No external funding. No conflicts of interest declared. Peer-review status: pending.