Nerve & Muscle Biopsy

Why tissue is sometimes necessary

Vasculitic neuropathy and inflammatory myopathy are treated with significant immunosuppression, often for years. Before committing a patient to that, the diagnosis should be as secure as it can be made. Several conditions imitate them closely: metabolic myopathies, drug-induced muscle injury, motor neurone disease and diabetic amyotrophy among others, and none of them respond to immunosuppression.

Muscle biopsy

A muscle is selected on the basis of examination, muscle enzyme levels and MRI — one that is affected but not yet destroyed, since end-stage muscle shows only scarring. A small sample is taken under local anaesthetic. The pathologist looks at where the inflammatory cells sit, which fibres are damaged, and specific staining patterns that separate dermatomyositis, polymyositis, inclusion body myositis and immune-mediated necrotizing myopathy.

Nerve biopsy

Usually the sural nerve at the ankle, chosen when nerve conduction studies show the asymmetric, patchy pattern that suggests vasculitis. It leaves a permanent patch of numbness on the outer side of the foot, which is why it is reserved for cases where the answer will change treatment.

After the procedure

Local wound care for a week or two, and normal activity resumed within a few days. Results take one to three weeks depending on the specialised stains required.

Conditions this is used for

These are the conditions in which Nerve & Muscle Biopsy forms part of the assessment or the treatment plan. It is not a complete list, and whether it applies to you is decided at consultation.

• ANCA-associated Vasculitis — GPA, MPA and EGPA
• Medium Vessel Vasculitis — Polyarteritis Nodosa (PAN)
• Cryoglobulinemic Vasculitis
• Dermatomyositis
• Polymyositis
• Immune-Mediated Necrotizing Myopathy (IMNM)

Whether a procedure is appropriate is decided during consultation, based on your symptoms, examination and existing reports.