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Inflammatory myopathies: dermatomyositis and myositis
Proximal symmetric weakness with a high CK points to an inflammatory myopathy; dermatomyositis also has a typical rash (Gottron, heliotrope) and requires a search for cancer; treatment is high-dose steroids with a steroid-sparing drug.
Why it matters in the exam
The question presents an adult who struggles to rise from a chair, climb stairs or lift the arms above the head, with a high CK, and sometimes a purple rash around the eyes (heliotrope), papules over the finger joints (Gottron) and a rash over the shoulders and upper back. Work-up: myositis antibodies, MRI of the muscles, EMG and muscle biopsy. Anti-Jo-1 defines the antisynthetase syndrome — interstitial lung disease, "mechanic's hands", arthritis and fever. In adult dermatomyositis (especially with anti-TIF1γ) a malignancy must be sought — ovary, lung, pancreas, stomach, bowel and breast.
Important differentials: inclusion body myositis in an older man — distal weakness of the finger flexors and quadriceps, poor response to steroids; statin myopathy — usually settles on stopping, but necrotising myopathy with anti-HMGCR antibodies continues after stopping and needs immune treatment; and PMR — pain and stiffness without true weakness and with a normal CK. In treatment: high-dose prednisone together with methotrexate or azathioprine, and IVIG in severe or refractory disease and in dermatomyositis. Swallowing and breathing are followed, and every patient has a lung check. Remember too that a normal CK does not fully exclude dermatomyositis — an "amyopathic" form with rash alone exists and still needs a cancer search and a lung check.
Key points
- Proximal symmetric weakness + high CK.
- Dermatomyositis: heliotrope, Gottron; search for cancer.
- Anti-Jo-1: ILD, mechanic's hands, joints, fever.
- Treatment: high-dose prednisone + methotrexate or azathioprine; IVIG.
- Separate from inclusion body, statin-related and PMR.
Summary table
| Disease | Clue | Test | Treatment |
|---|---|---|---|
| Dermatomyositis | Proximal weakness + heliotrope, Gottron | CK, anti-Mi-2, anti-TIF1γ, biopsy | Steroids + methotrexate or azathioprine; IVIG |
| Antisynthetase syndrome | ILD, mechanic's hands, arthritis, fever | Anti-Jo-1 | Steroids + sparing agent; treat the lung disease |
| Cancer search | Adult dermatomyositis | CT chest-abdomen-pelvis, mammogram, ovarian check, colonoscopy | Especially with anti-TIF1γ |
| Inclusion body | Older man, distal weakness (finger flexors, quadriceps) | Biopsy | Poor response to steroids |
| Statin-related | Weakness and high CK on a statin | Anti-HMGCR if it persists after stopping | Stop; immune treatment for necrotising myopathy |
| PMR (to separate) | Pain and stiffness, no true weakness | Normal CK, high ESR | Low-dose prednisone |
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Sources
- EULAR/ACR Classification Criteria for Adult and Juvenile Idiopathic Inflammatory Myopathies, 2017 — Clinical, laboratory and biopsy criteria
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Polymyositis, Dermatomyositis, and Inclusion Body Myositis
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.