A 28-year-old man presents with a 3-month history of hearing voices commenting on his actions, belief that his thoughts are being broadcast to others, and disorganized speech. He has no prior psychiatric history. Which investigation is most appropriate to exclude organic causes before confirming a diagnosis of schizophrenia?

## Investigation of Choice in First-Episode Psychosis ### Clinical Context When a patient presents with first-episode psychosis (FEP) meeting criteria for schizophrenia, the primary goal is to exclude medical/organic causes before attributing symptoms to a primary psychiatric disorder. ### Why Thyroid Function Tests and Metabolic Screening? **Key Point:** Thyroid dysfunction (especially hypothyroidism) and metabolic abnormalities (hypercalcemia, hyponatremia, hypoglycemia) are the most common reversible organic causes of psychosis in the general population. **High-Yield:** The standard workup for first-episode psychosis includes: 1. Complete blood count (CBC) 2. Urea, electrolytes, creatinine (U&E) 3. Liver function tests (LFTs) 4. Fasting glucose or HbA1c 5. Thyroid function tests (TSH, free T4) 6. Serum calcium and phosphate 7. Syphilis serology (RPR/VDRL) 8. HIV testing (if risk factors present) These investigations are **non-invasive, cost-effective, and high-yield** for detecting treatable causes. ### Comparison with Other Investigations | Investigation | Indication | Timing | |---|---|---| | **Thyroid/metabolic screening** | Routine in all FEP; detects reversible causes | **First-line** | | **MRI brain** | Suspected structural lesion, focal neurological signs, atypical presentation | Second-line; not routine | | **EEG** | Suspected seizure disorder, altered consciousness | Only if seizures suspected | | **Serum prolactin** | Baseline before antipsychotic; not diagnostic for schizophrenia | Supportive, not investigative | **Clinical Pearl:** Hypothyroidism can present with psychotic features, depression, and cognitive slowing—easily mistaken for schizophrenia. Correcting thyroid function may resolve psychosis entirely. ### Why Not the Other Options? - **MRI brain:** Indicated only if focal neurological signs, seizures, or atypical features (e.g., acute onset, rapid progression, age >40). Routine MRI in uncomplicated FEP is not cost-effective and does not change management in typical schizophrenia. - **EEG:** Not part of routine FEP workup unless seizure disorder is suspected (e.g., altered consciousness, myoclonic jerks). - **Serum prolactin:** Useful for baseline assessment before antipsychotics (which elevate prolactin), but does not help diagnose schizophrenia. Hyperprolactinemia is a side effect, not a cause of psychosis in this context. [cite:Harrison 21e Ch 386]