## Investigation of Secondary Hyperprolactinemia in Antipsychotic-Induced Cases ### Clinical Context Antipsychotics, particularly risperidone and paliperidone, commonly cause hyperprolactinemia by blocking D₂ receptors on lactotroph cells. However, before attributing elevated prolactin solely to the drug, other pathological causes must be excluded. ### Why TSH and Free T₄? **Key Point:** Hypothyroidism is the most common reversible secondary cause of hyperprolactinemia and MUST be screened before imaging or further workup. **High-Yield:** The mechanism is that TRH (thyrotropin-releasing hormone) stimulates both TSH and prolactin. In primary hypothyroidism, elevated TRH drives prolactin secretion independently of the antipsychotic effect. ### Investigation Algorithm for Drug-Induced Hyperprolactinemia | Investigation | Indication | Timing | |---|---|---| | **TSH + Free T₄** | Screen for hypothyroidism (most common reversible cause) | **First-line** | | **MRI pituitary** | If TSH normal AND prolactin >200 ng/mL OR neurological symptoms | Second-line | | **24-hr UFC** | Only if clinical signs of Cushing syndrome present | Not routine | | **LH/FSH** | Assess hypogonadism (consequence, not cause) | Tertiary | ### Clinical Pearl If TSH is elevated and free T₄ is low, treat hypothyroidism first—prolactin often normalizes without stopping the antipsychotic. This avoids unnecessary medication changes and psychotic relapse. **Mnemonic: SHRIMP** — Secondary causes to rule out before blaming antipsychotic: - **S**arcoidosis / **S**yphilis - **H**ypothyroidism ← *most common* - **R**enal failure - **I**diopathic hyperprolactinemia - **M**acroprolactinemia - **P**rolactinoma [cite:Harrison 21e Ch 375]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.