Inclusion Body Myositis

Synonyms:

a.k.a. inclusion body myopathy IBM

Diagnosis:

Clinical +Muscle biopsy +neurophysiology

Clinical features:

Usually >50 year old patients Progressive weakness of quadriceps, ankle dorsiflexors, finger flexors and facial muscles. Dysphagia is common.

Pathology, Muscle biopsy

Inflammation
HE: Rimmed vacuoles: Basophilic granules around vacuoles. Endomysial and perivascular lymphocytes. Increased connective tissue
GMT: rimmed vacuoles (red rim), ragged-red fibres, COX: COX negative fibres.
Congo red: amyloid in the rims
Immunohistochemistry: lymphocytes: CD8 positive. Amyloid deposits: beta amyloid, tau and ubiquitin positive
EM: tubulofilaments in cytoplasm and nucleus i.e. inclusions.

Findings on investigations:

CK: elevated or normal
EMG:

  • Myopathic
  • But mixed potentials (polyphasic units of short and long duration) occur

cN1a antibodies in inclusion body myositis
Hereditary forms:

  • VCP gene chr. 9p13-p12. Protein= Valosin-containing protein: IBM +Paget disease +Frontotemporal dementia IBMPFD
  • GNE gene mutation, protein= UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase,

Investigations to consider:

CK
EMG
Muscle biopsy

Monitor:

Weakness not CK

Treatment:

General measures:

  • Assistive devices and general support for complications

Some clinicians try:

  • IVIG, Prednisolone, methotrexate

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