Pupillocynetic Activity of Substance P in Systemic Sclerosis

OBJECTIVE: In systemic sclerosis (SSc), dysfunctions of peripheral nervous system (PNS) have been observed. Substance P (SP) instillation in human eye induces a cholinergic-independent pupil myosis. Pupil basal diameters (PBD) and pupil responsiveness to SP, expressed as area under the curve (AUC), were studied by pupillometry to assess SP-ergic fiber state and function in SSc. METHODS: Forty SSc patients [24 with limited (lSSc), 16 with diffuse (dSSc) disease] and 40 controls underwent pupillometric evaluation. After evaluation of PBD, SP 10-3 M was instilled in one eye and placebo in the contralateral eye. Antinuclear (ANA), anticentromere (ACA), and anti-Scl-70 autoantibodies were correlated with PBD and AUC. RESULTS: PBD was significantly lower in SSc patients versus controls (p < 0.001). PBD was minor in lSSc versus both dSSc and controls (p < 0.05), but no difference was found between dSSc and controls. In SSc, SP 10-3 M induced greater myosis compared to controls (p < 0.001). SP 10-3 M-induced myosis was higher in lSSc versus both dSSc and controls (p < 0.05). ACA significantly correlated with decreased values of PBD and AUC (p < 0.001). CONCLUSION: Our results show that PBD is reduced in patients with SSc and that SP induces a more intense myosis in SSc than controls. Moreover, in lSSc PBD is lower and SP increases the myosis in lSSc compared to dSSc and controls. This suggests a peculiar dysfunction of PNS in patients with the limited subset of SSc.