Background/Purpose: Scleromyositis (SM) is an emerging subgroup of autoimmune myositis associated with features of systemic sclerosis (SSc) and characterized by prominent vasculopathic features on ultrastructural evaluation of muscle capillaries. Yet, SM is also a frequent mimicker of immune-mediated necrotizing myopathy (IMNM) on muscle biopsy. Therefore, the aim of this study was to explore whether nailfold videocapillaroscopy (NVC) patterns in SM were distinct from IMNM.

Methods: A systematic review of NVCs from SM patients and IMNM controls was performed. In the absence of a gold standard or classification criteria, the clinical diagnosis of SM was based on expert opinion (consensus of ≥2 experts). Clinical, serological and pathological data were collected using a standardized protocol. NVC images were acquired using the DS MEDICA Videocap (200X magnification). Nailfolds of the 2nd, 3rd, 4th and 5th fingers of both hands were photographed by two experienced physicians (GG and MK) and scored by one of them (GG). Microhemorrhages, giant capillaries, ectasias and ramified capillaries were scored using a standardized semi-quantitative scale (0 = no, 1 = ≤33%, 2 = 33–66%, and 3 = ≥66% abnormalities/linear mm). Capillary density was scored both semi-quantitatively (0 if ≥7, 1 if 4–6, or 2 if ≤3 capillaries/mm) and quantitatively (mean number of capillaries/mm). Patterns were classified as SSc-active, SSc-like, non-specific abnormalities or normal. Each NVC parameter and the different NVC patterns were compared between SM and IMNM.

Results: 20 SM cases and 5 IMNM comparators (4 anti-HMGCR positive, 1 anti-HMGCR/anti-SRP negative) were included. SM patients were predominantly females (80%), mean duration from myositis diagnosis to NVC was 2±17 months and vasculopathic features included: Raynaud in 18/20 (90%), history of digital ulcers in 4/20 (20%) and pulmonary arterial hypertension in 1/20 (5%) patient. Sixty-five percent of SM patients fulfilled the ACR/EULAR SSc criteria at myositis diagnosis. SSc features leading to the diagnosis of SM in the remaining 7 patients included: positive ANAs and/or SSc-associated autoantibodies (n=7/7, 100%), Raynaud (n=5/7, 71%), interstitial lung disease (n=5/7, 71%), sclerodactyly (n=1/7, 14%) and SSc calcinosis (n=1/7, 14%). Giant capillaries, ramified capillaries and ectasia were present in 65%, 75% and 80% of SM subjects (median scores 0.16; 0.24 and 0.63, all p< 0.05 by Wilcoxon-Mann Whitney U test), respectively, and none of the IMNM controls. Capillary density was lower than normal (7.0-11.0/mm) in SM (median 4.9/mm) and significantly lower compared to IMNM controls (median 8.5/mm, p=0.012 by Wilcoxon-Mann Whitney U test). Seventy percent of SM patients had an SSc-active or an SSc-like NVC pattern (35% each), 15% had non-specific abnormalities and 15% were normal. Using the European NeuroMuscular Center pathological criteria, 29% of the SM muscle biopsies were classified as IMNM and 100% of these patients had an abnormal NVC whereas all NVCs were normal in IMNM controls.

Conclusion: An abnormal NVC may serve as a clue to support the diagnosis of SM in anti-SRP or anti-HMGCR negative patients presenting with histologic features of IMNM.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/scleromyositis-is-associated-with-nailfold-capillary-abnormalities-compared-to-immune-mediated-necrotizing-myopathy/