Cutaneous Nerve Laboratory
The Cleveland Clinic Cutaneous Nerve Laboratory, one of only a few in the country, has been created to improve diagnosis and research in small fiber sensory neuropathy.
Small fiber sensory neuropathy is a common neuromuscular disorder associated with many medical conditions, including diabetes mellitus, amyloidosis, HIV infection, connective tissue diseases, and pharmacological neurotoxicity. It is also not uncommon to be idiopathic, especially in elderly patients. The clinical presentation usually consists of cutaneous pain, numbness and autonomic dysfunction, which can lead to significant functional impairment. Some patients may predominantly present with pain, which is subjective. A sensitive and specific diagnostic tool is thus essential for making correct diagnosis and rendering appropriate subsequent management.
Small caliber nerve fibers consist of somatic (type C and Ad fibers) and autonomic fibers. They play key roles in cutaneous nociception, thermoreception, and autonomic function. Autonomic function can be assessed by quantifying sweat output and measuring cardiovascular regulation.
Since not all patients with small fiberopathy have both somatic and autonomic involvement, assessing somatic fibers is very much desired. These fibers are small and many are unmyelinated with very slow conduction velocities; therefore, their conduction responses cannot be captured and evaluated by routine nerve conduction studies. This gap has previously been filled by a histological method to evaluate cutaneous nerve fiber density. By immunostaining using the panaxonal marker, protein gene product 9.5 (PGP 9.5), of skin biopsies, intraepidermal small nerve fibers (IENF) become visible and can be assessed both morphometrically and morphologically.
IENF density evaluation is not only a powerful technique for diagnosing small fiber sensory neuropathy, but also a valuable tool for research of this disease. Since 3-mm punch skin biopsy is minimally invasive and well-tolerated, it can be safely repeated to monitor disease progression and treatment response. It has been used in the past to study neuropathies associated with various conditions, including diabetes mellitus, AIDS, leprosy, Fabry disease and postherpetic neuralgia. Trials are planned on small fiber neuropathy by using IENF density evaluation as one of the outcome measurements. This technique will also be useful in basic research to study molecular mechanisms underlying small fiber degeneration and regeneration to develop better clinical intervention.