Organic Mental Disorders: Medical and Neurological Causes, Assessment and Management

Organic mental disorder is an older teaching term for mental or behavioural symptoms caused by a demonstrable disease, injury, intoxication, withdrawal or physiological disturbance affecting the brain or body. Modern classifications use more specific terms such as delirium, major or mild neurocognitive disorder, substance/medication-induced disorder and mental disorder due to another medical condition. The important clinical message is unchanged: a new psychiatric presentation may be a medical emergency until reversible causes have been considered.

Learning objectives

• Define organic mental disorders and explain their relationship to current ICD and DSM terminology.
• Recognise medical, neurological, infectious, toxicological, endocrine and nutritional causes of psychiatric symptoms.
• Distinguish delirium, dementia/neurocognitive disorder, substance-induced syndromes and functional psychiatric illness.
• Plan a targeted assessment, investigation, treatment and prevention strategy.
• Communicate with family and document a safe formulation when the cause is not yet certain.

1. How medical disease produces psychiatric symptoms

2. Red flags for an organic cause

• Sudden onset, rapid progression or a waxing-and-waning course.
• Impaired attention, altered level of consciousness or disorientation that is disproportionate to the psychiatric symptoms.
• New onset at an atypical age, especially later life or childhood without developmental explanation.
• Fever, weight loss, night sweats, severe headache, meningism, rash, hypoxia or abnormal vital signs.
• Focal neurological findings, seizures, gait change, abnormal pupils, new incontinence or movement disorder.
• Visual hallucinations, olfactory hallucinations, fluctuating cognition or prominent cognitive decline.
• Recent head injury, pregnancy/postpartum state, immunosuppression, cancer, endocrine disease or new medicine.
• Exposure to alcohol, recreational drugs, pesticides, traditional medicines or occupational toxins.

3. Common causes to remember

3.1 Neurological

• Stroke, subdural haematoma, brain tumour, hydrocephalus and traumatic brain injury.
• Epilepsy, post-ictal states, non-convulsive status epilepticus and encephalitis.
• Alzheimer disease, Lewy-body disease, frontotemporal dementia, Parkinson disease dementia and vascular cognitive impairment.
• Multiple sclerosis, demyelination, autoimmune encephalitis and neurodegenerative disorders.

3.2 Infectious and inflammatory

• Sepsis, meningitis, encephalitis, HIV-associated disease, neurosyphilis, cerebral malaria and tuberculosis.
• Autoimmune encephalitis, vasculitis, systemic lupus and other inflammatory disease.
• Always combine exposure, immune status, fever, neurological findings and local epidemiology; no single negative test excludes every infection.

3.3 Endocrine, metabolic and nutritional

• Hypo- or hyperthyroidism, hypoglycaemia, diabetes emergencies, adrenal disease and severe electrolyte/calcium abnormalities.
• Renal or hepatic failure, hypoxia/hypercapnia, dehydration, malnutrition and B12/folate deficiency.
• Porphyria, Wilson disease and other rare metabolic conditions when the phenotype and age are suggestive.

3.4 Toxicological and medication-related

• Alcohol intoxication or withdrawal, opioids, sedatives, stimulants, cannabis, hallucinogens, inhalants and pesticides.
• Anticholinergics, corticosteroids, dopaminergic medicines, antimalarials, antiepileptics, sedatives, polypharmacy and abrupt withdrawal.
• Review herbal and traditional preparations without ridicule; composition and contamination may be uncertain.

4. Clinical assessment

1. Stabilise: ABCDE, observations, capillary glucose, oxygenation, temperature, hydration and level of consciousness.
2. Define onset: establish exact time course and compare with documented baseline.
3. Seek collateral: family, caregiver, school/work records, ambulance staff and previous notes.
4. Examine: general, cardiovascular, respiratory, abdominal and detailed neurological examinations, including gait and movements.
5. Review exposures: all medicines, recent changes, alcohol/drugs, toxins, infection risks, head injury and withdrawal.
6. Investigate the question: glucose, electrolytes/renal/liver tests, FBC, infection tests, thyroid/B12 and other targeted tests; ECG, CT/MRI, EEG or lumbar puncture when indicated.
7. Reassess: organic syndromes evolve. Repeat attention, arousal, observations and examination after treatment or time.

5. Delirium versus dementia versus functional illness

6. Investigations

6.1 Core tests when clinically indicated

• Capillary glucose, oxygen saturation, temperature and ECG when acute or unstable.
• Full blood count, electrolytes/urea/creatinine, calcium/magnesium, glucose, liver function and urinalysis.
• Thyroid function, B12/folate, HIV/syphilis, malaria, TB or other infection tests based on signs, risk and local protocol.
• Pregnancy test where relevant before radiation, teratogenic medicines or procedures.
• Toxicology and alcohol levels only when results will change care; interpret detection windows and false results.

6.2 Specialist investigations

• CT/MRI: focal deficit, head trauma, severe headache, seizure, new atypical psychosis, rapidly progressive cognition, cancer or immunosuppression.
• EEG: episodic altered awareness, seizures, post-ictal states, fluctuating unexplained symptoms or suspected encephalitis.
• Lumbar puncture: suspected meningitis/encephalitis, inflammatory disease or selected autoimmune presentations after contraindication assessment.
• Autoimmune/metabolic tests: guided by phenotype and specialist advice, not indiscriminate screening.

7. Management principles

• Treat the cause: oxygen, glucose, antibiotics/antimalarials, fluids, electrolyte correction, antidotes, seizure treatment, withdrawal management or surgery as indicated.
• Provide a safe environment: orientation cues, glasses/hearing aids, sleep protection, hydration, pain control, mobilisation and family presence where safe.
• Review and stop non-essential medicines that worsen cognition, sedation, anticholinergic burden or delirium.
• Use de-escalation and least-restrictive care. Medication for severe agitation is a last resort with airway, ECG and sedation monitoring.
• Rehabilitate cognition and function; plan caregiver support, follow-up, capacity and safeguarding.

8. Prevention

• Prevent infection, dehydration, hypoxia, constipation, urinary retention, uncontrolled pain and sleep deprivation.
• Medication reconciliation at admission, transfer and discharge; avoid unnecessary anticholinergic and sedative polypharmacy.
• Use orientation boards, clocks, daylight, familiar staff, hearing/vision aids and early mobilisation.
• Manage diabetes, hypertension, HIV, epilepsy, substance use and cardiovascular risk.
• Educate families about early change and when to seek urgent help.

9. Capacity and safeguarding

Organic illness can fluctuate. Assess capacity for each decision at the time it matters; delirium does not automatically remove all capacity, and a psychiatric diagnosis alone does not prove incapacity. Identify who can support communication and what lawful framework applies. Check for neglect, exploitation, financial abuse, medication misuse, unsafe driving, wandering, violence and caregiver exhaustion.

10. Worked cases

Case 1: Hypoactive delirium

An elderly patient becomes quiet, sleepy and inattentive after surgery. Do not mistake hypoactivity for depression. Check oxygen, glucose, infection, pain, medication and urinary retention; use a delirium tool and obtain collateral baseline.

Case 2: Steroid-related psychosis

A patient develops insomnia, grandiosity and hallucinations after high-dose corticosteroids. Assess for delirium, mood episode and medical complications; discuss dose reduction with the treating team and provide urgent psychiatric support if risk is high. Do not stop essential steroids independently.

Case 3: New psychosis with seizures

A young adult has hallucinations, memory disturbance and brief episodes of unresponsiveness. The combination is a neurological red flag. Arrange urgent medical/neurological assessment, EEG and targeted investigations rather than assuming a primary psychotic disorder.

11. Quick self-test

1. Why is “organic mental disorder” now used less often as a final diagnosis?
2. Name six red flags for a medical or neurological cause.
3. How does delirium differ from dementia in onset and attention?
4. What bedside test should be performed early in acute behavioural change?
5. When are CT/MRI, EEG or lumbar puncture considered?
6. Why is collateral history essential?
7. List four preventable contributors to delirium.
8. What is the priority treatment for an organic mental syndrome?

Answers

1. It is broad and can obscure the specific cause; modern classifications use more precise diagnoses such as delirium, neurocognitive disorder or substance/medication-induced disorder.
2. Sudden/fluctuating onset, impaired attention, abnormal vitals, fever, focal neurology, seizures, head injury, atypical age, immunosuppression and new medicines/substances are examples.
3. Delirium is acute and fluctuating with impaired attention; dementia is usually progressive over months/years with attention relatively preserved early.
4. Capillary glucose, together with ABCDE, observations, oxygen saturation and level of consciousness.
5. For focal deficits, head injury, severe headache, seizures, atypical/rapid psychosis or cognition, encephalitis, immunosuppression and persistent unexplained symptoms.
6. The patient may be confused, amnestic or unable to describe the baseline and time course; family can identify acute change and function.
7. Dehydration, hypoxia, infection, pain, constipation, urinary retention, sleep deprivation and sedative/anticholinergic polypharmacy.
8. Stabilise and treat the underlying medical, neurological, toxicological or metabolic cause while protecting safety and function.

References and further reading

• WHO. Clinical descriptions and diagnostic requirements for ICD-11 mental, behavioural and neurodevelopmental disorders.
• NICE. Delirium: prevention, diagnosis and management.
• WHO. mhGAP Intervention Guide, version 2.0.
• WHO. mhGAP guideline for mental, neurological and substance use disorders, 2023.
• Use Uganda Ministry of Health and hospital protocols for malaria, HIV, TB, poisoning, safeguarding, referral and emergency care.