Leg muscle reflexes mediated by cutaneous A-beta fibres are normal during gait in reflex sympathetic dystrophy

Objectives: Reflex sympathetic dystrophy (RSD) is, from the onset, characte rized by various neurological deficits such as an alteration of sensation a nd a decrease in muscle strength. We investigated if afferent A-beta fibre- mediated reflexes are changed in lower extremities affected by acute RSD. Methods: The involvement of these fibres was determined by analyzing reflex responses from the tibialis anterior (TA) and biceps femoris (BF) muscles after electrical stimulation of the sural nerve. The reflexes were studied during walking on a treadmill to investigate whether the abnormalities in g ait of the patients were related either to abnormal amplitudes or deficient phase-dependent modulation of reflexes. In 5 patients with acute RSD of th e leg and 5 healthy volunteers these reflex responses were determined durin g the early and late swing phase of the step cycle. Results: No significant difference was found between the RSD and the volunt eers. During early swing the mean amplitude of the facilitatory P2 response s in BF and TA increased as a function of stimulus intensity (1.5, 2 and 2. 5 times the perception threshold) in both groups. At end swing the same sti muli induced suppressive responses in TA. This phase-dependent reflex rever sal from facilitation in early swing to suppression in late swing occurred equally in both groups. Conclusions: In the acute phase of RSD of the lower extremity there is no e vidence for abnormal A-beta fibre-mediated reflexes or for defective regula tion of such reflexes. This finding has implications for both the theory on RSD pathophysiology and RSD models, which are based on abnormal functionin g of A-beta fibres. (C) 2000 Elsevier Science Ireland Ltd. All rights reser ved.