Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.
Recognise dermatomyositis across skin tones, detect clinically amyopathic and organ-threatening phenotypes, direct muscle, lung and malignancy assessment, and prevent scarring, calcinosis and treatment harm.
Dermatomyositis is an immune-mediated microvascular and interface disease of skin, skeletal muscle and sometimes lung, swallowing, heart and other organs. Skin can precede weakness, occur with active myositis or persist in clinically amyopathic disease. Gottron lesions and heliotrope change are the most recognisable clues, but scalp scale, poikiloderma, nailfold capillary loss, mechanic hands and cutaneous ulceration may provide the first route to diagnosis.
Visible colour varies across pigmentation. Erythema may be red, violaceous, grey-brown or predominantly hyperpigmented; oedema, scale, telangiectasia, dyspigmentation and distribution should be recorded explicitly. Pruritic scalp disease can be mistaken for psoriasis or seborrhoeic dermatitis, while Gottron papules may be overlooked as dark knuckle change. Palpating scale and examining cuticles with magnification reduces inequitable under-recognition.
Skin phenotype predicts extracutaneous risk imperfectly. Anti-MDA5 disease can have little muscle enzyme elevation yet severe ILD. Anti-TIF1-gamma and several clinical variables shape malignancy assessment in adult onset. Treatment therefore starts with organ mapping, not a topical prescription alone. Photoprotection and local therapy relieve limited skin disease; objective weakness, dysphagia, lung disease, ulceration or persistent severe skin activity requires rheumatology–dermatology systemic treatment and rehabilitation.
Complement, interferon and cellular immune pathways injure skin and muscle microvasculature in a genetically susceptible person.
Myositis-specific antibodies correlate with differing skin, lung, muscle and malignancy risks but do not create disease without a compatible phenotype.
In some adults an antitumour immune response cross-reacts with regenerating tissue, linking disease onset to an occult or recent malignancy.
Ultraviolet light exposure aggravates epidermal interface inflammation and shapes the shawl, V-neck and other characteristic photodistributed cutaneous patterns.
Immune attack at basal epidermis produces scale, pigment alteration, telangiectasia and atrophy across characteristic extensor and light-exposed sites.
Systemic microangiopathy creates giant nailfold loops, visible haemorrhage and progressive capillary loss and also contributes to perifascicular muscle injury.
Inflammation and ischaemic signalling injure proximal muscle, reducing force for rising, climbing, lifting, swallowing and breathing.
Selected phenotypes, especially anti-MDA5 disease, drive aggressive interstitial lung injury even when muscle enzymes and strength remain near normal.
Flat-topped scaly violaceous, red-brown or hyperpigmented papules lie over metacarpophalangeal and interphalangeal joints and may fissure.
Upper eyelids show violaceous, dusky or grey-brown colour with oedema, sometimes more evident as swelling than erythema.
Shawl, V-neck and lateral-thigh areas develop mixed pigment, telangiectasia, scale and atrophy with photosensitive worsening.
Ragged cuticles, periungual erythema, giant loops, haemorrhage and capillary loss support systemic microvascular involvement.
Hyperkeratotic fissured radial fingers and palms can signal antisynthetase overlap, especially with arthritis, Raynaud phenomenon or lung disease.
Painful ulcers over Gottron sites or nailfolds and palmar papules raise rapidly progressive ILD concern even without weakness.
Difficulty rising, climbing, lifting or holding the neck reflects symmetrical shoulder and hip-girdle weakness and requires organ-level myositis assessment.
Photosensitive interface disease can overlap, but Gottron lesions, muscle weakness, nailfold changes and myositis antibodies favour dermatomyositis.
Scaly scalp and knuckle disease may mimic common dermatitis, but eyelid oedema, poikiloderma and systemic features require broader assessment.
Raynaud phenomenon and capillary loss overlap, while sclerodactyly, fingertip ulcers and progressive skin thickening define a different connective-tissue pattern.
Statin injury, glucocorticoid weakness, thyroid disease and other toxic or metabolic causes lack the coherent characteristic cutaneous signs.
Slow asymmetric finger-flexor and knee-extensor weakness in later life, often with modest enzymes, responds poorly to ordinary immune treatment.
Bulbar and respiratory-muscle weakness causes unsafe swallowing, aspiration pneumonia, weak cough, nocturnal hypoventilation and ventilatory collapse.
Inflammatory and fibrotic lung injury ranges from indolent restriction to rapidly progressive hypoxic failure, particularly in anti-MDA5 disease.
Adult-onset disease can signal cancer near diagnosis, with risk modified by age, symptoms, phenotype and antibodies.
Chronic inflammation can leave calcium deposits, ulceration, contracture, poikiloderma and muscle fatty replacement despite later immune control.
Glucocorticoid and steroid-sparing therapy causes infection, metabolic, bone, blood, liver, lung and reproductive harms requiring structured surveillance.
Characteristic lesions may appear months before weakness, creating an opportunity for lung, swallow and cancer assessment before other organs declare themselves.
Amyopathic anti-MDA5 disease can have normal enzymes yet life-threatening interstitial lung progression, so phenotype and respiratory testing outrank reassurance.
Gottron papules can appear dark brown or grey with fine scale in richly pigmented skin and deserve palpation, nailfold examination and systemic history.
Cutaneous lupus and dermatomyositis overlap histologically, making distribution, muscle, nailfold and antibody context indispensable.
Objective loss of proximal power is measured during tasks and examination; severe fatigue can coexist but should not substitute for strength assessment.
Dismissing dark scaly knuckles as friction without checking Gottron morphology and nailfolds.
Using a normal CK to exclude dermatomyositis or MDA5-associated lung disease.
Treating scalp and facial disease topically while failing to ask about swallowing and breathlessness.
Interpreting one commercial myositis antibody line as diagnostic without a compatible phenotype.
Giving methotrexate daily instead of weekly or omitting blood, liver, renal and pregnancy safeguards.
Applying a single lifelong whole-body cancer scan schedule rather than risk- and symptom-adapted assessment.
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A patient has scaly violaceous papules over the finger joints, dusky oedematous upper eyelids and new difficulty rising from a chair. Which diagnosis best unifies these findings?
National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.
Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes
Use lower potency on eyelids, face and folds and monitor atrophy, telangiectasia, infection and total area; topical control cannot replace lung, muscle, swallow and malignancy assessment.
Response is variable and dermatomyositis patients can develop drug eruptions. Review retinal, renal, cardiac, QT, glucose and interaction risk and stop and reassess a new widespread rash.
Never administer daily. Monitor FBC, liver and renal function; avoid pregnancy, significant liver disease, serious infection and trimethoprim or co-trimoxazole, and investigate new cough or breathlessness urgently.