Which Scale Best Detects Treatment Response of Tremor in Parkinsonism?

Background: Several scales are available for rating the severity of tremor at present. However, the sensitivity to change of these instruments has remained to be clarified. Objective: To compare the sensitivity of the Fahn-Tolosa-Marin Tremor Rating Scale, the Part III of the Movement Disorder Society-sponsored Unified Parkinson's Disease Rating Scale (MDS-UPDRS) and the MDS-UPDRS Tremor Scale to the effects of various antitremor treatments. Methods: Enrolling subjects with parkinsonism associated with tremor, we analyzed two scenarios: (1) tremor changes associated with acute levodopa challenge (n = 287) and (2) a 12-month outcome of different treatment options (n = 512) including deep brain stimulation (n = 146), levodopa/carbidopa intestinal gel infusion (n = 30), and initiating (n = 63) or adjusting oral antiparkinsonian medication (n = 273). Changes in tremor scales were assessed by effect size values (Cohen's d and eta-square). Results: Part B of the Fahn-Tolosa-Marin Tremor Rating Scale was the most sensitive to acute levodopa challenge (Cohen's d = -1.04, eta(2) = 0.12). However, Part A of the Fahn-Tolosa-Marin Tremor Rating Scale showed the highest effect size, which was a small one (Cohen's d = -0.33, eta(2) = 0.03), for detecting a treatment-related change in the severity of tremor during long-term follow-up. Conclusions: The Fahn-Tolosa-Marin Tremor Rating Scale has a better ability to capture changes due to levodopa challenge or antiparkinsonian treatment than MDS-UPDRS Part III or MDS-UPDRS Tremor Scale.