Huntington's disease (HD) is an autosomal dominant inherited neurodegenerative disorder, beginning in adulthood. HD represents the majority of patients who present the triad of motor, cognitive and psychiatric symptoms. The last two may be early manifestations, but the clinical diagnosis is based on motor symptoms and a positive genetic test for CAG repeat extension. The remaining patients that are negative for the HD genetic mutation may have HD phenocopies.

Illustrate the role of psychiatric assessment, discuss the psychiatric and behavioural manifestations, and management.

Illustrate the challenge of diagnosing HD in psychiatry.

A literature search was performed on PubMed database. The patient clinical record was reviewed.

We report a case of a 49-year-old male with a family history of HD (mother, uncle, cousin). He was diagnosed with a psychotic disorder fifteen years ago, hospitalised twice and thereafter treated as an outpatient with fluphenazine long-acting injection. He was a symptomatic for ten years. During the last year, he started showing dysphoria, marked irritability, stammering, inappropriate behaviour, poorly structured paranoid delusions, mild cognitive impairment and lack of insight. This was correlated with the beginning of functional impairment, both professionally and socially. Further assessment was performed: neurological evaluation, head CT scan and the genetic test was negative. He is clinically stable under haloperidol long-acting injection.

HD is a rare condition which is frequently under diagnosed, especially in early stages, due to lack of recognition of psychiatric symptoms. HD-like disorders should be considered if the clinical picture is obvious, but HD gene test result is negative.

The authors have not supplied their declaration of competing interest.