Objective: Description of a clinical case of extra-pyramidal features in a patient with myotonic dystrophy type 1.

Background: Myotonic dystrophy type 1 (MD-1) is an autosomal dominant muscular dystrophy, caused by abnormal expansion of unstable CTG trinucleotide repeats in the DMPK gene, with a multisystemic clinical syndrome, including additional ocular, cardiac, endocrine and cognitive involvement. Tremor can be a rare symptom.

Method: Case report.

Results: A 73-year old man, with a past medical record of vascular risk factors and atrial fibrillation, presented to the outpatient clinic with a 5-year history of upper limb tremor and progressive slowness of movements. On examination, he had slight bilateral ptosis and facial palsy, marked symmetric postural and rest hand tremor, left predominant slowness of movements and slight rigidity, postural instability and distal muscle weakness, with steppage gait. He had a family history of myotonic dystrophy type 1 but he had not been tested. Parkinsonism was suspected and levodopa was initiated, with only subjective clinical improvement. Subsequent study with needle electromyography demonstrated myotonic discharges, more proeminent in distal muscles. The genetic study revealed expansions of CTG repeats on the DMPK gene, which confirmed the diagnosis of MD-1. Due to clinical doubts, DaTSCAN imaging was requested and revealed to be normal.

Conclusion: Extrapyramidal manifestations have been increasingly recognized in patients with MD-2. Its description in MD-1 is restricted to a few case reports. The pathophisiology of these symptoms in MD remains poorly understood, but central nervous system involvement is suspected. In our case, postural and rest tremor was the presenting feature, along with symptoms suggestive of parkinsonism. Despite subjective response to levodopa treatment, DaTSCAN imaging didn’t confirm presynaptic dopaminergic deficit. This suggests a tremor syndrome similar to essential tremor with the confounding effects of muscle weakness, although the reported levodopa response is intriguing. Further studies are needed to better understand extrapyramidal features in MD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/myotonic-dystrophy-type-1-presenting-as-postural-tremor/