Reversible intermittent rhythmic myoclonus with fluoxetine in presumed Pick's disease

A 61-year-old man with presumed Pick's disease was successfully treated with fluoxetine for pathological affect. Severe intermittent, rhythmically repetitive trains of myoclonus developed suddenly the following year. A dystonic-like component involving the shoulder region and a decrescendo frequency pattern were observed. Myoclonus involved the face, palate, shoulder, neck, upper chest and back, diaphragm, hips, and upper extremities, especially on the right side. Movements were not influenced by postural adjustments, startle, or other stimuli. Movements proved insensitive to benztropine but abated with discontinuation of fluoxetine. Rechallenge with fluoxetine or trazodone evoked the movements, whereas clonazepam and chloral hydrate abolished the movements. The pattern of myoclonus is unlike previous reported cases and may relate to activation of serotonin 5HT1A receptors (possibly supersensitive in Pick's disease) or to hypodopaminergia. Although fluoxetine may be useful as adjunct therapy in dementing disorders, caution may be warranted in its use in Pick's disease.