When is a muscle biopsy necessary?

A muscle biopsy is necessary only in exceptional cases to diagnose ALS. In rare instances, it is not possible to reliably distinguish between ALS and a muscle disorder based solely on a clinical examination and additional diagnostic tests (electromyography, laboratory tests, and biomarkers). In such cases, a muscle biopsy may be useful to rule out a muscle disorder (myopathy) with greater certainty.

A muscle biopsy can generally distinguish between muscle changes associated with myopathies (muscle disorders) and muscle damage typical of ALS (neurogenic damage pattern). Although ALS is not a muscle disease, the reduced nerve supply to the muscles (denervation) leads to characteristic changes in the cellular structure of the muscle tissue (neurogenic changes). Due to the invasive nature of a muscle biopsy (incision of the skin and removal of a pea-sized piece of muscle tissue, followed by neuropathological analysis), muscle biopsy is not part of “routine diagnostics” for ALS. In most cases, the clinical symptoms, in combination with non-invasive supplementary diagnostic tests, are sufficient to confirm a diagnosis of ALS and make a muscle biopsy unnecessary.