Serotonin syndrome in a case of depression with various somatic symptoms: The difficulty in differential diagnosis

A 65-year-old female patient with major depressive disorder suffered from clonus, shivering and impaired visual acuity after 20 mg/day of paroxetine administration. The symptoms were initially regarded as further manifestations of her somatic symptoms of depression, and paroxetine was increased to 30 mg/day resulting in frequent clonus, increased shivering, serious dysarthria, ongoing impairment in visual acuity and agitation. These symptoms subsided upon paroxetine discontinuation. Ten mg/day of paroxetine rechallenge provoked dysarthria, tremor and headache, but these symptoms improved again upon paroxetine discontinuation. These findings indicate that the patient's symptoms were not somatic in origin but were in fact the symptoms of serotonin syndrome. In conclusion, the present case suggests the difficulty in diagnosing serotonin syndrome in a patient with somatic symptoms.