Diagnostic problems in Huntington's chorea and tardive dyskinesia.

W HEN THE CLINICIAN encounters a demented adult patient with choreiform movements he is likely to think of the diagnosis of Huntington’s chorea. However, when the family is inconclusive and the patient has been medicated with neuroleptic agents, the diagnosis of tardive dyskinesia, the late and frequently permanent complication of neuroleptics, must also be considered. How confidently can this differential diagnosis be made? An answer to this question will be sought by reviewing and comparing (1) the significant epidemiologic data, (2) the clinical descriptions, (3) the psychologic symptomatology, (4) associated drug use, (5) the speculated pathophysiologic mechanisms, (6) the presumptive pharmacologic diagnostic tests, (7) the neurochemical findings, (8) the radiographic and postmortem findings, and (9) other findings of both Huntington’s chorea and tardive dyskinesia. The following case history illustrates the difficulty that is sometimes encountered when attempting to differentiate between Huntington’s chorea and tardive dyskinesia.