Objective: To characterise adult-onset isolated unilateral LLD and examine the relationship between clinical findings and presynaptic dopaminergic imaging.

Background: Adult-onset lower limb dystonia (LLD) may raise suspicion of an underlying neurodegenerative disorder, particularly Parkinson’s disease (PD), although early clinical differentiation can be difficult.

Method: We retrospectively analysed patients referred to a tertiary movement disorders centre. Only individuals with isolated unilateral LLD were included. Patients with exposure to dopamine receptor blocking agents were excluded. Clinical records were reviewed to extract phenomenology, triggers, neurological findings, treatment response and follow-up. Blinded video assessments of finger and toe tapping were independently performed by two movement disorders neurologists unaware of clinical data and imaging results. Slowness and decrement were rated for each limb.

Results: Nine patients with adult-onset isolated unilateral LLD were identified. Mean age at onset was 45.3 years (range 20–61). Most patients (78%) reported insidious onset with gradual progression, whereas two (22%) described a subacute onset. Mean follow-up was 6.9 years (median 4, range 2–18). The most common dystonic posture was plantar flexion with ankle inversion (6/9, 67%). On blinded video assessment, slowness during tapping tasks was identified in a small number of patients and showed variability between raters. No patient demonstrated decrement on either finger or toe tapping. Presynaptic dopaminergic imaging was performed in eight patients and showed reduced putaminal uptake in two (25%). In these patients, clinical bradykinesia was not detectable on blinded tapping assessment. Both underwent levodopa trials and reported worsening of dystonia.

Conclusion: Adult-onset isolated unilateral LLD most commonly presented with insidious onset and gradual progression. A minority of patients showed abnormal presynaptic dopaminergic imaging. In these cases, clinical bradykinesia was not detectable on blinded examination and levodopa trials were associated with worsening of dystonia. These findings highlight the heterogeneity of adult-onset LLD and suggest that clinical examination and levodopa response may not reliably reflect dopaminergic imaging abnormalities.

References: Chang, F.C.F., Josephs, K.A., 2013. Levodopa Responsiveness in Adult-onset Lower Limb Dystonia is Associated with the Development of Parkinson’s Disease. Tremor and Other Hyperkinetic Movements 3, 03. https://doi.org/10.5334/tohm.136
Schneider, S.A., Edwards, M.J., Grill, S.E., Goldstein, S., Kanchana, S., Quinn, N.P., Bhatia, K.P., Hallett, M., Reich, S.G., 2006. Adult‐onset primary lower limb dystonia. Movement Disorders 21, 767–771. https://doi.org/10.1002/mds.20794
Ramdhani, R.A., Frucht, S.J., 2013. Adult-onset Idiopathic Focal Lower Extremity Dystonia: A Rare Task-Specific Dystonia. Tremor and Other Hyperkinetic Movements 3, 03. https://doi.org/10.5334/tohm.135

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MDS Abstracts - https://www.mdsabstracts.org/abstract/adult-onset-isolated-lower-limb-dystonia-clinical-phenomenology-and-dopaminergic-imaging-correlates/