Extremity Pain in a Patient with Diffuse Muscle Weakness: A Clinical Picture Orchestrated by Two Uncommon Mutations

ABS TRACT This case report presents a 36-year-old female presenting with burning lower extremity pain, proximal muscle weakness, and imbalance.Her clinical examination revealed diffuse proximal weakness, with mild distal involvement, and left ptosis.Routine laboratory and imaging results were unremarkable, and electromyography showed mild diffuse myopathic involvement.Muscle biopsy demonstrated non-inflammatory myopathy with Type 1 fiber predominance and Type 2 atrophy.Using next-generation sequencing, we identified a novel heterozygous SCN9A c.1941+8T>C variant, classified as likely pathogenic and associated with paroxysmal extreme pain disorder, and a heterozygous TPM3 c.737C>T (p.Ser246Leu) variant, consistent with congenital fiber-type disproportion myopathy.The management of the case consisted of physical therapy and analgesics.This case highlights the importance of integrating genetic testing with histopathological evaluation in atypical neuromuscular presentations.