CUTANEOUS NERVE-FIBER DEPLETION IN VIBRATION WHITE FINGER

Vibration white finger or hand-arm vibration syndrome is the episodic blanching of the fingers in response to cold occurring in those who wo rk with hand held vibrating tools. Clinically the condition differs fr om primary Raynaud's phenomenon as persistent paraesthesiae and pain a re common in the hands and arms and these occur independently from the 'white attacks'. Symptoms can become severe enough to warrant a chang e of occupation. Industrial compensation may be awarded for vibration white finger but, at present, no simple or reliable objective diagnost ic test is available. Calcitonin gene-related peptide (CGRP) is a neur opeptide with powerful vasodilator properties. A deficiency of immunor eactive CGRP nerve fibres has been previously demonstrated in the digi tal cutaneous microvasculature of patients with primary and secondary Raynaud's phenomenon with the distribution and quantity of other types of nerve fibres not being significantly altered. To determine if the innervation of the cutaneous microvasculature in vibration white finge r was also abnormal skin biopsy samples from the fingers of 15 patient s with vibration white finger, six healthy age matched controls who wo rked with vibrating machinery and 26 healthy age matched controls who were heavy manual workers without exposure to vibrating machinery were examined by immunohistochemistry. To try to correlate any histologica l abnormalities with clinical neurological deficit sensory nerve condu ction studies have so far been performed in six patients with vibratio n white finger. There was a significant reduction in both the number o f CGRP and protein gene product 9.5 (PGP) immunoreactive nerve fibres in the digital cutaneous biopsies from the patients with vibration whi te finger when compared to the biopsies from the heavy manual workers and the healthy workers exposed to vibration. The pattern of the loss of CGRP immunoreactive nerve fibres was similar to that described prev iously in Raynaud's phenomenon and may account for the episodic vasosp asm seen in both conditions. PGP is a constitutive protein of all nerv es therefore the reduced PGP immunostaining indicates generalized stru ctural. neuronal damage which could account for the persistent pain an d paraesthesiae characteristic of vibration white finger. The nerve co nduction studies revealed sensory nerve action potentials within the l ow range of normal in five patients with vibration white finger and mi ld median nerve compression in the remaining patient implying that the neuronal damage in the patients with vibration white finger is confin ed mainly to the small unmyelinated nerve fibres. The immunohistochemi cal findings may provide the basis far a diagnostic test for vibration white finger.