Background/Purpose: Myositis with significant B-cell infiltrates on muscle biopsy has scarcely been described in adults. Radke (2018) found B cells in adult dermatomyositis (DM) and stratified them as classic, B-cell-rich and follicle-like DM. In patients without DM, three neuropathology studies described myositis with significant B-cell infiltrates. De Bleeker (1996) reported 7 patients with biopsies showing nodules resembling lymph nodes, i.e. a B-cell-rich center surrounded by CD4+ T-cell-rich peripheral zone; notable findings were cervical muscle weakness and the presence of a connective tissue disease (CTD). Pestronk (2006) described 9 patients with prominent perimysial and perivascular B-cell infiltrates, cervical muscle weakness and either myasthenia gravis or a CTD. Espitia-Thibault (2017) studied 4 patients with primary Sjögren syndrome (SS) and myositis; and found germinal centre-like structures composed predominantly of CD4+ T cells and B cells. The aim of the present study was to describe the clinicoserological findings of patients with B-cell-rich infiltrates on muscle biopsy, and no DM.

Methods: Muscle biopsies with significant B-cell infiltrates (≥ 30 CD20+ cells/aggregate) were identified from 2 neuropathology centers. All cases were reviewed in multidisciplinary meetings. Clinical, serological, pathological features and classification criteria for inclusion body myositis (IBM) were recorded. Patterns of muscle involvement were noted, including cervical, finger flexor and quadriceps weakness. The presence of a CTD and cancer within 3 years of myositis diagnosis was also recorded. Patients with a DM rash were excluded.

Results: Ten patients with myositis, no DM rash, and significant B-cell infiltrates on muscle biopsy were included. Nine were female; median age at myositis diagnosis was 66.5 years (range 51-85). Median CK level was 291 UI/L (range 98–4372). Two patients with normal strength, but myalgias (n=1) or cervical muscle edema (n=1), had imaging suggestive of myositis. All remaining patients had cervical muscle weakness (n=8), and 3 had objective oropharyngeal dysphagia. Quadriceps (n=6) and finger flexor (n=3) weakness was noted, and 4 patients met the Lloyd IBM classification criteria. Associated diseases included anti-CCP positive RA (n=3), systemic sclerosis (SSc) (n=3), primary SS (n=1), systemic lupus erythematosus (n=1) and lung cancer (n=1). Serologically, all patients but one were tested: none had myositis-specific autoantibodies (aAbs) and 2 patients with SSc had anti-Th/To (n=1) and anti-PM-Scl (n=1) aAbs. Anti-Ro52/TRIM21 (n=4), anti-SSA/Ro60(n=3), anti-SSB/La (n=2) were present. Anti-NT5c1A aAbs were present in 1 of 3 tested patients.

Conclusion: Myositis and significant B-cell infiltrates were associated, as in previous studies, with various CTDs, and not only with SS. Cervical weakness and features of IBM were frequent in this subset of patients. CD20 stains were listed as optional in the 205^th European Neuromuscular Centre international workshop. Routine CD20 staining should be considered in patients with cervical muscle weakness and suspected myositis in the setting of an associated CTD.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/b-cell-rich-inflammatory-myopathies-in-adults-striking-association-with-connective-tissue-diseases/