Case report: A patient with brachio-cervical inflammatory myopathy was misdiagnosed as flail arm syndrome

Abstract

Brachio-cervical inflammatory myopathy (BCIM) is a rare inflammatory myopathy characterized by dysphagia, bilateral upper limb atrophy, limb-girdle muscle weakness, and myositis-specific antibody (MSA) negativity. BCIM has a low incidence and is commonly associated with autoimmune diseases. We present a case report of a 55-year-old man with progressive upper limb weakness and atrophy, diagnosed with flail arm syndrome (FAS). The initial electromyography revealed extensive spontaneous muscle activity and increased duration of motor unit potentials (MUPs). During follow-up, evidence of myogenic damage was observed, as indicated by a decreased duration of MUPs in the right biceps muscle. Laboratory and genetic testing ruled out hereditary or acquired diseases. Negative serological antibodies for myasthenia gravis. Hereditary or acquired diseases were ruled out through laboratory and genetic testing. Whole-body muscle magnetic resonance imaging (MRI) showed extensive edema and fat replacement in the bilateral upper limbs, scapular, and central axis muscles, while the lower extremities were relatively mildly affected. Muscle biopsy revealed numerous foci of inflammatory cells distributed throughout the muscle bundle, with predominant CD20, CD138, and CD68 expression, accompanied by a light infiltration of CD3 and CD4 expression. The muscle weakness improved with the combination of oral prednisone (initially 60 mg/day, tapered) and methotrexate (5 mg/week) treatment.

Keywords: brachio-cervical inflammatory myopathy; case report; flail arm syndrome; misdiagnosis; myositis.

Figure 1

During the second admission, the patient had mild atrophy of the lingual muscles (A), severe atrophy of both forearms (B), upper arms (C), and trapezius muscles (D) with concomitant shoulder collapse (E), with preserved muscle volume in both lower extremities (F) (white arrows).

Figure 2

The muscles of the tongue showed mild lipoatrophy [(A), green arrows]. Both the upper arm and forearm muscles exhibited bilateral asymmetric edema and lipoatrophy (B, C). Edema was observed in the right biceps, lateral femoral, and gastrocnemius muscles (orange arrows) (D). Atrophy was present in the trapezius and psoas muscles (E). Severe fat replacement was noted in the dorsal muscles (F, G). The volume of muscle in the lower extremities was preserved, with only slight involvement of the lateral group of thigh muscles compared to the posterior group of calf muscles (H, I). T1-weighted imaging: green arrow; short-tau inversion recovery (STIR) MRI: orange arrow.

Figure 3

In the HE staining, numerous foci of inflammatory cells were observed in the muscle tissue [(A, B), red and yellow arrows]. Immunohistochemical staining revealed that the foci were mainly composed of CD20+ B cells (C) and CD68+ macrophages (D), accompanied by some CD138+ plasma cells (I) and a small number of CD4+ and CD8+ T cells (E, H). Additionally, some myofibers exhibited heterogeneous NADH enzyme activity (F), and C5b-9 was observed beneath the membrane of certain muscle fibers (G).