- Design
- Single-centre method comparison study
- Population
- 20 muscle biopsies, inflammatory and non-inflammatory myopathies
- Primary outcome
- Concordance of paraffin vs frozen immunohistochemistry
- Effect
- MHC-II and MxA 90%, p62 80%; MHC-I and MAC failed on paraffin
This small study developed an immunohistochemistry method for formalin-fixed paraffin muscle sections and compared it with frozen sections in 20 cases, including dermatomyositis, inclusion body myositis, immune-mediated necrotising myopathy and non-inflammatory controls. It was published in June 2026.
MHC-II, MxA and p62 stained comparably on paraffin and frozen sections, with agreement of 90%, 90% and 80%. Discrepancies involved a single marker in each case and may reflect patchy disease. MHC-I and membrane attack complex staining did not work on paraffin sections.
Many laboratories, including most in India outside neuromuscular centres, receive muscle biopsies already in formalin. This offers a partial answer: MxA supports dermatomyositis and p62 supports inclusion body myositis on paraffin. But MHC-I, the most widely used screening stain, still needs frozen tissue.
- Ask clinicians to send part of every muscle biopsy fresh for freezing where possible.
- Consider MxA, MHC-II and p62 on paraffin sections when only formalin-fixed muscle is available.
- Do not rely on MHC-I or membrane attack complex staining in paraffin muscle; both failed here.
- State in the report when frozen tissue was unavailable and which stains were therefore limited.
Why it matters
A formalin-fixed muscle biopsy need not be a wasted biopsy.
Don't overread it
Twenty cases from one laboratory; the method needs validation before it replaces frozen-section work-up.
The statistics, in plain English
Agreement of 90% in 20 cases means two disagreements; with numbers this small, the true agreement could be considerably lower.
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