Autosomal Dominant Slow Channel Congenital Myasthenia Presenting as Limb Girdle Weakness

Document Type

Conference Proceeding

Publication Date

4-2025

Publication Title

Neurology

Abstract

Background: Congenital myasthenic syndromes classically present with fatigable weakness, ptosis and delayed motor milestones. A limb girdle type of congenital myasthenia can be difficult to diagnose and can often be mistaken for a myopathy or a muscular dystrophy due to the lack of ocular symptoms. Limb girdle weakness has previously been described in autosomal recessive congenital myasthenia syndromes.

Design/Methods: We discuss the case of a 39-year-old male presenting with progressive asymmetric bilateral arm weakness for 2 years. He recalled having a “floppy neck” as an infant. He had chronic minimal dysphagia, no ptosis, diplopia, or dyspnea. On examination, he was noted to have mild bilateral temporal atrophy, non-fluctuating bilateral ptosis, facial muscle weakness, and significant neck flexion weakness. His voice was normal. His motor exam revealed bilateral scapular winging, atrophy of the bilateral forearm and hand muscles, and asymmetric proximal and distal upper extremity weakness, with involvement of wrist and finger extension and thumb abduction. Initial NCS was normal although a double peak appearance of CMAPs was later noted. Electromyogram showed a myogenic pattern with early recruitment, decreased amplitude and duration of the MUAPs in multiple upper extremity muscles. CK was normal. Genetic testing with a panel of over 200 genes for neuromuscular disorders was positive for a pathogenic mutation within the CHRNA1 gene that is associated with a slow channel congenital myasthenic syndrome. Repeat electrodiagnostic studies revealed decrement in amplitudes of more than 10% with repetitive nerve stimulation confirming the diagnosis. The patient was then started on fluoxetine for treatment.

Results: NA

Conclusions: Slow channel congenital myasthenic syndrome can present with adult-onset limb girdle weakness. It is important to obtain broad genetic testing when suspecting a genetic cause of weakness to avoid missing the diagnosis. Broad genetic testing in our patient resulted in identifying the correct diagnosis and initiating treatment promptly.

Volume

104

Issue

7, Suppl 1

First Page

3926

Comments

American Academy of Neurology (AAN) Annual Meeting, April 5-9, San Diego, CA

Last Page

3926

DOI

10.1212/WNL.0000000000211333

ISSN

1526-632X

Link to Full Text

Share

COinS