Assessing small-fiber sensory neuropathy: quantitative sensory testing and sural nerve biopsy

Sensory neuropathies involving small-fibers (mostly the unmyelinated axons) are frequently encountered in systemic disorders, including diabetes mellitus, the most prevalent ones. Conventional evaluation includes nerve conduction studies (NCS), which access predominantly large myelinated fibers. Other approaches include quantitative sensory testing (QST) and nerve biopsy. We evaluated the clinical feasibility of these methods for neuropathic patients. Neuropathic patients had higher detection thresholds for cold- and warm-sensations than normal subjects. The differences were more obvious in the lower limbs than in the upper limbs, consisting with the idea of length-dependent process of neuropathy. Nerve biopsy is valuable in evaluating of the pathology of neuropathy, exhibiting varying degrees of demyelination and Wallerian-like degeneration. The loss of unmyelinated fibers is recognizable by nerve biopsy, although a quantifying procedure is necessary for objective assessment of the severity of neuropathy. We conclude that multi-disciplinary approaches including QST, NCS, nerve biopsy and skin biopsy, which is under developing, will provide complementary information for better diagnosis and understanding of small-fiber sensory neuropathy.