Polymyositis

Case contributed by Dr Bruno Di Muzio

Presentation

Severe progressive proximal muscle weakness associated with CK rise to 343.

Patient Data

Age: 51-year-old
Gender: Female
MRI

MRI bilateral thigh (myositis protocol)

Bilateral patchy areas of high T2/STIR signal intensity in muscles diffusely, most prominently at the left gluteus maximus and right > left quadriceps. No asymmetry muscular fatty atrophy. Small right femoral head subchondral cystic change. Conclusion: Findings are in keeping with active myositis.

Case Discussion

Imaging appearances are non-specific, differentials are broad and include: 

  • inflammatory myopathies
    • dermatomyositis
    • polymyositis
    • inclusion body myositis
    • eosinophilic myositis
    • proliferative myositis 
  • myositis associated with connective tissue diseases
    • systemic lupus erythematosus (SLE)
    • Sjögren syndrome
    • overlap syndrome
    • scleroderma
    • mixed connective tissue disease

This MRI was performed prior to muscle biopsy, which revealed: 

MICROSCOPIC DESCRIPTION: Paraffin and Cryostat sections show a moderate variation in muscle fibre diameters. There is multifocal endomysial and perimysial infiltration by mononuclear inflammatory cells with multiple foci of myophagia. Inflammatory cells are a mixture of T lymphocytes (CD8>CD4) and monocyte-macrophages. There are no actively degenerating or necrotic fibres. Several regenerating fibres are seen. There is no fibre vacuolation. Three COX negative fibres are noted. There is no evidence of myofibrillar disorganisation. ATP'ase staining shows a normal random distribution of fibre types. There is no lipid stasis or excess accumulation of glycogen in muscle fibres and the activity of glycolytic enzymes is normal.

DIAGNOSIS: "Left thigh muscle biopsy": Inflammatory immune myopathy (IIM) with endomysial and perimysial pathology most consistent with polymyositis.

COMMENT: It is noted that the patient has high titres of rheumatoid factor and antinuclear antibodies but no anti-Ro or anti-Jo antibodies. Testing for antibodies against signal recognition particle (SRP) is recommended. Immunohistochemistry for MHC Class I and II and C5b-9 (MAC) is pending.

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Case information

rID: 50910
Case created: 27th Jan 2017
Last edited: 12th Jun 2017
Tag: rmh
Inclusion in quiz mode: Included

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