Isolated vocal tremor as a focal phenotype of essential tremor: a retrospective case review

BACKGROUND Essential tremor (ET) is a common condition associated with significant physical and psychosocial disability. "Classic" ET is a clinical syndrome of action tremor in the upper limbs and less commonly the head, jaw, voice, trunk, or lower limbs. Current diagnostic criteria for ET exclude isolated vocal tremor (IVT). Failure to recognize IVT as a form of ET may contribute to misdiagnosis and missed opportunities for treatment. METHODS We conducted a retrospective review of cases referred for voice disturbance. Patients with a primary diagnosis of vocal tremor were included while those with a diagnosis of spasmodic dysphonia where excluded. RESULTS 19 cases of vocal tremor were identified, of which 17 patients (89%) were female. The average age of vocal symptom onset was 64 (SD 8.0) and patients had been symptomatic an average of 6 years (SD 4) at their initial visit. 8 patients had IVT while 11 also had evidence of subtle head or limb tremor. 8 patients (42%) had a family history of ET, with vocal tremor specifically identified in 5 of those cases (26%). 11 patients (58%) noted transient tremor improvement after alcohol consumption. Primidone and propranolol were the most common medications prescribed to these patients prior to consultation. 7 patients were given a trial of 1 gm of sodium oxybate in the office as part of a clinical trial, with at least mild improvement in vocal tremor noted by qualitative assessment. CONCLUSIONS ET may present as vocal tremor with little or no associated limb tremor. It may be a more common manifestation of ET in women. A family history of tremor and improvement in tremor after consuming alcohol can often be elicited on history. We propose that IVT may be part of the spectrum of ET.