[Extreme atrophy of the shoulder muscles in juvenile ankylosing spondylitis as a (misleading) main symptom].

An extreme unilateral muscular atrophy of the shoulder and upper arm region was a symptom of juvenile ankylosing spondylitis in a 20-year-old female patient. No pathological patterns were found in electromyographic, bioptic, and tomographic (CT, NMR) investigations. The muscular atrophy was caused by a shoulder arthritis with severe erosive damage. The false assumption of a neurological disorder and the disregard of anamnesis and low back pain delayed for several years an accurate diagnosis. After the onset of an arthritis of hip joints a collagen disease with myositis was supposed falsely in spite of normal electromyographic results. The unusual muscular atrophy around the shoulder joint probably must be interpreted as a consequence of reflex inhibition and partly due to inactivity. A real myositis seems to not be probable, because newer investigations in contrast to earlier findings show no evidence for inflammatory muscle disease in ankylosing spondylitis.