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Título

Congenital myasthenic syndrome with distal myopathic phenotype

RESUMO

Case presentation: A 50-year-old male with bipolar disorder was evaluated due to a progressively-worsening weakness that began 34 years ago. Weakness was predominantly distal and asymmetrical (right > left), involving his upper-limbs and causing fine motor activities impairment. He evolved with neck extensor weakness and dysphagia. Physical examination revealed predominantly distal and right-sided weakness in his upper-limbs with bilateral atrophy of thenar, hypothenar and interosseous muscles. EMG showed proximal and distal post-synaptic neuromuscular junction disease associated with distal upper-limb myopathy. Family history revealed a similar condition in his paternal grandmother, father and two daughters. Genetic test yielded Congenital Myasthenic Syndrome (CMS) related to a mutation in the CHRNA 1 gene. Discussion: CMSs include a group of neuromuscular diseases of genetic origin with variable genotype and phenotype. Clinically, patients present fatigability, transient or permanent weakness of the extrinsic ocular, facial, bulbar, trunk, respiratory or limb muscles. Symptoms usually start in childhood and may be present from birth or more rarely in adolescence. The CMS 1A is related to a mutation in the CHRNA1 gene and has an autosomal dominant character, but with variable penetrance and expression, explaining the different phenotypes. Mutations occur in the acetylcholine receptor (AChR) subunits causing a delay of the opening time of the acetylcholine ion channel that are located at the neuromuscular junction. CMS 1A should be suspected in patients of any age who present weakness and fatigability of the scapular, cervical and dorsal forearm (wrist and finger extensors) muscle groups in which there is no response to the use of cholinesterase inhibitors or the worsening of symptoms. The diagnosis is based on the symptomatology and on the electroneuromyography findings that demonstrate a decrease in the repetitive stimulus; the dosage of anti-AChR antibody can also be performed. Final comments: CMS with myopathic phenotype is a rare presentation, with only a few cases described in the literature with different phenotypes in the same family. Our patient had the distal myopathic phenotype while his two daughters had CMS of the slow channel type with mutation in the same gene.

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Doenças Neuromusculares