A 45-year-old man presents with myotonia (difficulty releasing grip), proximal weakness predominantly affecting hip flexors, and multisystem features

Question

A 45-year-old man presents with myotonia (difficulty releasing grip), proximal weakness predominantly affecting hip flexors, and multisystem features including cataracts, myalgia, and tremor. Unlike myotonic dystrophy type 1, his facial muscles are spared. EMG shows myotonic discharges. Genetic testing shows a CCTG tetranucleotide repeat expansion in the CNBP (ZNF9) gene. What is the diagnosis?

Accepted Answer

Myotonic dystrophy type 2 caused by a CCTG repeat expansion in the CNBP gene

Answer

Paramyotonia congenita caused by a pathogenic SCN4A variant affecting sodium channels

Answer

Myotonia congenita caused by a pathogenic CLCN1 variant affecting chloride channels

Answer

Non-dystrophic myotonia without the multisystem features of a repeat-expansion disorder

Answer

Myotonic dystrophy type 1 caused by a CTG repeat expansion in the DMPK gene

Myotonic Dystrophy Type 2 – PROMM — SCE Neurology MCQ