Traditionally, from the days of Charcot in the 1860s, a definitive diagnosis of a neuromuscular condition (nerve conditions, or neuropathy; muscle conditions, or myopathy; and manifestations of a more general abnormality such as vasculitis) was obtained by pathological examination of nerve or muscle tissue obtained by biopsy.
Nowadays, other less invasive investigations are available to aid diagnosis, including neurophysiology, nerve conduction studies, electromyography, a host of blood tests, and, of course, a vast array of genetic tests. Many conditions that in the past we would have been unsure about can now be diagnosed by blood tests.
So the key question is: When do we need to perform a nerve or muscle biopsy? For which conditions is the traditional pathological examination of nerve or muscle tissue obtained by biopsy absolutely necessary, and for which conditions is another investigation more useful, and biopsy can therefore be avoided?