Coexisting sporadic late onset nemaline myopathy and AL amyloid myopathy – incidental or related?

Orly Moshe-Lilie, George Banks, Eva Medvedova, Ahmad Masri, Nizar Chahin

Research output: Contribution to journalArticlepeer-review

Abstract

Sporadic late onset nemaline myopathy (SLONM) and amyloid myopathy are frequently unrecognized acquired and treatable myopathies, which classically present with rapidly progressive and severe proximal muscle weakness. We report a case of SLONM and amyloid myopathy associated with IgM lambda monoclonal gammopathy in a 77-year-old Caucasian man. Creatine kinase (CK) was mildly elevated. Myositis panel was negative. Electromyogram showed prominent fibrillation potentials and positive sharp waves with myopathic motor unit action potentials. Muscle biopsy revealed nemaline rods and amyloid deposits with characteristic apple-green birefringence under polarized light, and liquid chromatography tandem mass spectroscopy detected a peptide profile consistent with AL (lambda) type amyloid deposition. Genetic testing for congenital nemaline rod myopathy was negative. The patient was treated with dexamethasone and chemotherapy x3 cycles with very good partial remission. CK and lambda light chain normalized. Our case emphasizes the importance of completing a thorough histochemical and pathological evaluation by muscle biopsy analysis, to provide timely and optimal treatment of these conditions.

Original languageEnglish (US)
Pages (from-to)533-538
Number of pages6
JournalNeuromuscular Disorders
Volume32
Issue number6
DOIs
StatePublished - Jun 2022

Keywords

  • AL amyloidosis
  • Amyloid myopathy
  • Monoclonal deposition related disorders
  • SLONM
  • Sporadic late onset nemaline rod myopathy

ASJC Scopus subject areas

  • Pediatrics, Perinatology, and Child Health
  • Neurology
  • Clinical Neurology
  • Genetics(clinical)

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