What is the appropriate medical workup for a patient presenting with psychosis, including auditory, visual, and tactile hallucinations and delusional parasitosis?

Medical Workup for Psychosis with Auditory, Visual, Tactile Hallucinations and Delusional Parasitosis

All patients presenting with psychotic symptoms including hallucinations and delusional parasitosis must undergo a thorough physical and neurological evaluation to rule out general medical conditions before attributing symptoms to a primary psychiatric disorder 1.

Essential History Components

Obtain detailed information on:

• Symptom presentation and timeline: Onset, duration, progression of hallucinations (auditory, visual, tactile) and delusional beliefs 1
• Substance use history: Screen for amphetamines, cocaine, hallucinogens, phencyclidine, alcohol, marijuana, solvents, stimulants, corticosteroids, and anticholinergic agents—illicit drug use is the most common medical cause of acute psychosis 1, 2
• Recent head trauma, seizures, or new/worsening headaches: These suggest CNS lesions or seizure disorders 1, 2
• Recent infections or fever: Consider encephalitis, meningitis, or HIV-related syndromes 1
• Developmental history and premorbid functioning: Important for distinguishing primary psychiatric disorders 1
• Family psychiatric history: Focus on psychotic illnesses and mood disorders 1

Physical and Neurological Examination

Perform comprehensive assessment including:

• Vital signs: Tachycardia or severe hypertension suggests drug toxicity or thyrotoxicosis; fever may indicate encephalitis or porphyria 2
• Complete neurological examination: Assess for focal deficits, coordination, gait, involuntary movements, abnormalities of motor tone 1
• Skin examination: Look for stigmata of self-injury, excoriations from scratching (common in delusional parasitosis), or evidence of drug use 1, 3
• Mental status examination: Document thought content and process, perceptual disturbances, mood, level of anxiety, and cognitive function 1

Laboratory Testing

Basic workup should include:

• Complete blood count (CBC) 1
• Comprehensive metabolic panel (including renal and hepatic function) 1
• Thyroid function tests (TSH, free T4) 1, 2
• Urinalysis 1
• Urine toxicology screen 1, 2
• Vitamin B12, folate, and niacin levels 2
• Calcium and parathyroid hormone 2

Additional testing based on clinical presentation:

• HIV testing and syphilis serology if risk factors present 1, 2
• Ceruloplasmin and 24-hour urine copper if Wilson's disease suspected (especially in younger patients with neuropsychiatric symptoms) 1
• Chromosomal analysis if clinical features suggest developmental syndrome (e.g., velocardiofacial syndrome) 1

Neuroimaging

For new onset psychosis without neurologic deficits:

• CT head without contrast is usually appropriate as initial imaging, though diagnostic yield is very low (0-1.5%) in patients without focal neurologic signs 1
• MRI brain without contrast is preferred when clinical picture is unclear, presentation is atypical, or there are abnormal examination findings 1
• MRI is more sensitive for detecting small infarcts, encephalitis, temporal lobe lesions, multiple sclerosis, and subtle structural abnormalities 1

Neuroimaging is more strongly indicated if:

• Focal neurologic deficits are present 1
• First episode of psychosis in older adults (>40 years) 4
• Subacute onset suggesting oncologic cause 2
• History of head trauma or seizures 1, 2

Electroencephalography (EEG)

Order EEG when:

• Evidence of neurological dysfunction on examination 1
• History of seizures or seizure-like activity 1
• Fluctuating level of consciousness suggesting delirium 1

Special Considerations for Delusional Parasitosis

The combination of tactile hallucinations (formication) with delusional parasitosis requires:

• Rule out primary dermatologic conditions through careful skin examination 3, 5
• Consider secondary causes: Substance use (especially stimulants like cocaine and methamphetamine), neurologic disorders, dementia, or medical conditions 5, 6, 7
• Screen for comorbid psychiatric disorders: Depression, anxiety, or other psychotic disorders 5, 6
• Assess for shared psychotic disorder (folie à deux) if family members report similar symptoms 5

Differential Diagnosis Priority

The workup must systematically exclude:

1. Substance-induced psychosis (most common medical cause) 1, 2
2. Delirium from metabolic, infectious, or toxic causes 1
3. CNS lesions: Tumors, infarcts (especially temporal lobe), congenital malformations, head trauma 1
4. Seizure disorders 1
5. Infectious diseases: Encephalitis, meningitis, HIV, syphilis 1, 2
6. Metabolic/endocrine disorders: Thyrotoxicosis, endocrinopathies, Wilson's disease, porphyria 1, 2
7. Neurodegenerative disorders: Huntington's disease, metachromatic leukodystrophy 1
8. Autoimmune conditions: Systemic lupus erythematosus, multiple sclerosis 1
9. Mood disorders with psychotic features: Bipolar disorder and psychotic depression commonly present with hallucinations and delusions 1

Common Pitfalls

Visual hallucinations are more suggestive of medical/organic causes than auditory hallucinations, which are more typical of primary psychiatric disorders 2. The presence of visual hallucinations in your patient warrants particularly thorough medical workup 2, 8.

Cognitive changes, abnormal vital signs, and visual hallucinations together strongly suggest a medical rather than primary psychiatric etiology 2.

Substance abuse comorbidity is extremely high (up to 50%) in adolescents and young adults with psychosis, making repeated toxicology screening important even if initial screen is negative 1.

Longitudinal reassessment is essential as misdiagnosis at initial presentation is common, particularly between schizophrenia and bipolar disorder 1.