Objective: To assess the efficacy of apomorphine in identification of levodopa responsive atypical parkinsonism.

Background: Management of atypical parkinsonism is a challenge. Most of these patients end up with suboptimal trial of levodopa due to preconceived notions about the levodopa response in atypical parkinsonism, sometimes without any clear documentation of benefits. Can apomorphine, a short and rapid acting dopamine receptor agonist segregate these patients and thereof limit potential misuse of levodopa? Management of atypical parkinsonism is a challenge. Most of these patients end up with suboptimal trial of levodopa due to preconceived notions about the levodopa response in atypical parkinsonism, sometimes without any clear documentation of benefits. Can apomorphine, a short and rapid acting dopamine receptor agonist segregate these patients and thereof limit potential misuse of levodopa?

Method: Subjects diagnosed with atypical parkinsonism underwent apomorphine response test (ART). Those who showed at least 50% improvement on UPDRS III scores were considered to have positive response. The further response of these subjects to escalated levodopa dosages were reviewed.

Results: Nineteen atypical parkinsonism subjects (M:F- 15:4) with a mean age of 65.2 years (Range:51-75years) and duration of symptoms of 41.7 months (Range:4-84months) underwent ART.  Clinical diagnosis in these subjects included Multiple system atrophy (n-3), Progressive supranuclear palsy (n-4), Vascular parkinsonism (n-1), Atypical atypical parkinsonism (n-11). All of these subjects had poor/no subjective response to levodopa at assessment except for three.   6/19 subjects showed good response to ART (including one with partial subjective benefits). They included MSA (n-1) and Atypical atypical parkinsonism (n-5) with clinical response of 77.3%, 72.1%, 63.6%, 61%, 50% and 49.5% respectively on UPDRS III scores. Following escalation of levodopa in these six subjects 3 reported subjective benefits (LD dosage: 750mg,750mg,850mg), two were lost to followup and in one no benefit was noted (LD dosage:1500mg).

Conclusion: In atypical parkinsonism patients, ART can be used as potential instrument to assess whether escalation in levodopa can benefit their clinical symptoms. It also acts as biofeedback both to the patient, caregiver and physician to try higher dosages than conventional levodopa trials.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/apomorphine-as-a-diagnostic-tool-to-identify-levodopa-responsive-atypical-parkinsonism/