LAUSR

A 41-year-old male Chinese patient had an incidental finding of elevated serum creatine kinase (4000 U/L, normal range 2–200 U/L) during a routine physical examination 3 years ago, which fluctuated between 300 and 400 U/L in a series of re-examinations. The patient presented with proximal extremities weakness 2 years ago. A physical examination showed a waddling gait. Volume reduction of the right gluteus was found. The proximal muscle strength of the extremities was 4/4 and bilateral distal muscle strength was 5/5, according to the Medical Research Council scale of muscle strength. Serum anti-Ku antibodies were positive on a myositis-specific antibody examination. Chest computed tomography suggested right diaphragm elevation. A electromyogram showed proximal muscle myogenic damage. Muscular magnetic resonance imaging showed intramuscular fat infiltration in the erector spinae muscles and thigh muscles, predominantly extensor muscles. In addition, right vastus medialis oedema was found (Figure 1). A muscle biopsy from the right quadriceps femoris showed scattered muscle fibre atrophies combined with rimmed vacuoles (RVs) (Figure 2). The patient had a previous history of total thyroidectomy and radioactive iodine-131 therapy for thyroid cancer. Until now, his thyroid function has been normal with thyroxine replacement. Anti-Ku antibodies were originally reported to relate to scleroderma–polymyositis (SSc-PM) (1). With increasing reports, other rheumatological disorders, for example, inflammatory myopathies (IMs) (2), were considered to be related to anti-Ku antibodies. According to the previous studies, IMs with anti-Ku antibodies usually present with proximal and axial muscle weakness and atrophy accompanied by some rheumatological manifestations, such as arthritis, Raynaud’s phenomenon, interstitial lung disease, dermatosclerosis, and granuloma formation (2–5). Our patient showed predominant involvement of axial and proximal muscles. However, this is the first report of a case involving the diaphragm, which is a respiratory muscle in the axial muscle group, in association with anti-Ku antibody IM. Histologically, RVs occur most frequently in inclusion body myositis (IBM), and also in a range of other myopathies (6). IMs with anti-Ku antibodies mainly display typical myositis, while a minority have features of IBM (2, 3). The distribution of weakness and antibody tests help to distinguish IMs with anti-Ku antibodies from IBM. Apart from the involvement of axial and proximal muscles, the distribution of weakness includes the flexor digitorum profundus and other distal muscles in IBM (7). Furthermore, anti-cN1A antibodies are found in some IBM patients (8). Taken together, the diagnosis was confirmed as IM with anti-Ku antibodies in the present patient.