One case at a time.

Fever, tachycardia, chest pain and a troponin twenty times the upper limit three weeks into clozapine are clozapine-induced myocarditis until proved otherwise; it usually appears in the first four to eight weeks, often looks like a flu-like illness, and can be fatal. Clozapine is stopped at once and the patient is referred for urgent cardiac assessment, including an echocardiogram. Treating it as an infection while continuing clozapine, with antibiotics or blood cultures, keeps giving the drug that is damaging the heart. A lower dose does not stop a hypersensitivity myocarditis.

Reference: Stern, T. A., Wilens, T. E., & Fava, M. (Eds.). (2025). Massachusetts General Hospital comprehensive clinical psychiatry (3rd ed.). Elsevier.

Fluctuating alertness with subtle facial twitching, and no metabolic or toxic cause, raises non-convulsive status epilepticus, which can look exactly like delirium; an EEG is the test that shows it, and it is urgent. MRI looks for structural causes and is not the first step for suspected seizures. A lumbar puncture is for suspected infection or inflammation, which nothing here suggests. Heavy metal screening needs an exposure history.

Reference: Stern, T. A., Wilens, T. E., & Fava, M. (Eds.). (2025). Massachusetts General Hospital comprehensive clinical psychiatry (3rd ed.). Elsevier.

Normal development to 18 months, then loss of purposeful hand use with stereotyped hand-wringing, an unsteady gait and slowing head growth, in a girl, is the pattern of Rett syndrome, caused in most cases by a mutation in the MECP2 gene, so genetic testing is the next step. During the regression social engagement may fall away enough to look like autism spectrum disorder, and DSM-5-TR asks for the known genetic condition to be named rather than the picture labeled autism alone. An autism diagnosis with behavioral therapy names the regression without investigating its cause. Risperidone treats irritability, which she does not have, and leaves the regression unexplained. Hearing and vision screening is for delayed speech, not for a regression with hand stereotypies and slowing head growth.

Reference: American Psychiatric Association. (2022). Neurodevelopmental disorders. In Diagnostic and statistical manual of mental disorders (5th ed., text rev.). American Psychiatric Association Publishing.

Believing that his wife has been replaced by an identical impostor, while he stays warm to her voice on the phone, is Capgras syndrome, a delusion of misidentification. In an older person it should prompt a search for a neurodegenerative or other organic cause, since it occurs in Lewy body and Alzheimer's dementia and after brain injury as well as in schizophrenia. Fregoli syndrome is the reverse: strangers are believed to be a familiar person in disguise. Cotard syndrome is a nihilistic delusion about the self. Delusional jealousy is a belief in a partner's infidelity, not her replacement.

Reference: Stern, T. A., Wilens, T. E., & Fava, M. (Eds.). (2025). Massachusetts General Hospital comprehensive clinical psychiatry (3rd ed.). Elsevier. p. 311.