An Unusual Presentation of Serotonin Syndrome and Subsequent Catatonia in a Patient With a Family History of Huntington’s Disease

Neuroleptic malignant syndrome (NMS) and serotonin syndrome (SS) represent serious life-threatening conditions that share phenotypic and pathophysiologic features due to intricate interactions between the dopaminergic and serotoninergic systems. Malignant catatonia’s underlying pathophysiological mechanisms are poorly understood, but it is clinically difficult to distinguish it from NMS. Huntington’s disease (HD) is an autosomal dominant neurodegenerative disorder characterized by CAG expansion in exon 1 of the huntingtin (HTT) gene. Even though involuntary movements and lack of coordination are pivotal in HD, psychiatric manifestations are an integral part of it and may precede the emergence of chorea by years. The overlap in symptoms is noticeable for SS and NMS and distinguishing between the two may be challenging if exposure to both dopamine antagonists and serotoninergic agents exists. We present the case of a 48-year-old woman with an unusual presentation of serotonin syndrome and subsequent catatonia possibly overlapping with a neurodegenerative disorder, HD. This case report offers an interesting interconnection between three different syndromes that have tight pathophysiological and phenotypical associations.