Small-Fiber Nerve Biopsy
Indications For Nerve Biopsy
Nerve biopsy can identify potentially treatable causes of neuropathy, such as vasculitis, atypical CIDP, sarcoidosis, amyloidosis, lymphomatosis, or leprosy, when other tests fail to diagnose these conditions. Given that it is an invasive test, however, a nerve biopsy is usually only recommended when the neuropathy is progressive, threatens to become debilitating, and other tests fail to identify a cause. (Oh, 1990; Midroni and Bilbao, 2006; Schroder, 1998). Vasculitis, amyloidosis, sarcoid and other multifocal disorders may also affect skeletal muscle so that biopsy of muscle in addition to nerve may increase the diagnostic yield.
Location Of The Nerve Biopsy
In cases where the neuropathy affects the lower limbs, the superficial peroneal nerve with the peroneus brevis muscle, or the sural nerve with the vastus lateralis or gastrocnemius muscle are usually examined. When only the upper limbs are affected, the superficial radial nerve or a branch of the ulnar nerve in the dorsum of the hand can be biopsied (Said, 2002a; Ruth et al, 2005; Bevilacqua et al, 2007). Targeted biopsy of a sensory rootlet in demyelinating sensory radiculopathy (Sinnreich et al, 2004), or of the obturator nerve branch to the gracilis muscle in multifocal motor neuropathy (Corbo et al, 1997; Riva et al, 2011) have also been described.
The biopsy nerve samples are prepared in three different ways to fully assess the tissue for diagnostic purposes. One nerve piece (0.5 cm in length) is fixed in 10% formalin and embedded in paraffin; a second piece of similar length is transported in Michel's medium and frozen in the laboratory using liquid nitrogen; and a third piece (2.0 to 2.5 in length) is placed in glutaraldehyde fixative for preparation of semithin plastic sections and teased myelinated nerve fibers.