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