Purpose of review: To help clinicians to distinguish between myositis (and other immune-mediated and immunosuppressant-responsive disorders) and its many clinical mimics.
Recent findings: Increasing experience has shown that findings from conventional investigations, such as muscle biopsy, can be misleading. More specialist investigations, notably autoantibody screening, immunocytochemical techniques, and evolving DNA technologies, are powerful tools but experience is currently largely limited to specialist centres - and even these techniques are open to misinterpretation.
Summary: Misdiagnosis is hazardous to the patient. Treatable conditions may be missed, or patients subjected inappropriately to potentially toxic drug treatments. Judicious use of clinical skills alone should help reduce these risks.