Abstract:

OBJECTIVES: To report cases of chronic autoimmune necrotizing myopathy with anti-signal recognition particle antibodies (anti-SRP myopathy) initially misdiagnosed as muscular dystrophy, in particular, facioscapulohumeral muscular dystrophy (FSHD).
METHODS: Medical records of patients with anti-SRP myopathy in our institution were retrospectively reviewed.
RESULTS: All 6 patients were initially diagnosed with muscular dystrophy because of the long-term clinical course and lack of inflammation on biopsy; 5 were diagnosed with FSHD based on a winged scapula. However, the following features suggested an alternative diagnosis, leading to anti-SRP antibody measurement: (1)lack of family history, (2) lack of facial involvement and asymmetry, (3) prominent dysphagia, and (4) profuse spontaneous activities on needle electromyography. All patients showed improvement with immunomodulating therapy.
CONCLUSIONS: Anti-SRP antibody measurement should be considered in patients diagnosed with FSHD if they present with diagnostic hallmarks of anti-SRP myopathy listed above, to avoid oversight of this potentially treatable disorder.

日本語要旨:

抗SRP抗体を伴う自己免疫介在性壊死性ミオパチー(抗SRPミオパチー)患者で、長期経過と筋病理における炎症が見られないことから、当初は筋ジストロフィーと診断されていた6例を報告した。内５例は、翼状肩甲を呈したことから顔面肩甲上腕型筋ジストロフィー(FSHD)と診断されていた。しかし、家族歴がない事、筋力低下に左右差が目立たないこと、重度の嚥下障害等の所見から、抗SRPミオパチーが疑われ、抗体測定により抗SRPミオパチーの診断が確定した。これらの症例は、非典型的FSHD症例においては抗SRP抗体測定を考慮する必要性があることを示している。