Dermatomyositis

Published on 02/04/2015 by admin

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63 Dermatomyositis

Instruction

Examine this patient.

Salient features

History

• The adult form usually occurs after the age of 40 years

• Weakness of proximal muscles evolving over weeks or months: difficulty in getting from a low chair or squatting position, climbing stairs, lifting and running

• Inability to raise head

• Dysphagia (caused by weakness of the muscles of the pharynx)

• Muscle pain and tenderness

• Raynaud’s phenomenon

• Ask the patient whether the red rash is made worse by exposure to sunlight

• Skin features (Fig. 63.1):

• Heliotrope rash or purplish-blue rash around the eyes, back of the hands, dilated capillary loops at the base of fingernails, erythema of knuckles accompanied by a raised violaceous scaly eruption (Gottron’s sign); the erythema spares the phalanges (unlike that of SLE in which the phalanges are involved and the knuckles are spared)

• Erythematous rash may be present on the neck and upper chest (often in the shape of a V), shoulders (shawl sign), elbows, knees and malleoli

• Cuticles may be irregular, thickened and distorted; the lateral and palmar areas of the fingers become rough and cracked with irregular ‘dirty’ horizontal lines, resembling those in a mechanic’s hands.

Note: In dermatomyositis, the myopathy is accompanied by a rash, which includes three classic types:

• Gottron’s sign: a papulosquamous eruption on the dorsum of the fingers

• Heliotropic rash: a violaceous discoloration over the eyelids and face

• ’Shawl’ rash: an erythematous eruption over the anterior chest and upper torso.

• Muscle features:

• Proximal muscle weakness and tenderness of muscles (muscle wasting absent or minimal)

• Weakness of neck flexors in two-thirds of cases

• Intact or absent deep tendon reflexes.

Fig. 63.1 Characteristic dermatomyositis skin changes. (A) Linear erythema (Gottron’s sign). (B) Scalp rash. (C) V sign. (D) Shawl sign.

(With permission from Firestein et al. 2008.)

Proceed as follows:

• If the patient is >40 years, tell the examiner that you would like to look for an underlying neoplasm.

• Look for interstitial lung disease (occurs in 5–10% of patients with polymyositis or dermatomyositis, especially in those with anti-Jo-1 antibody).

Diagnosis

This patient has Gottron’s papules and proximal muscle weakness (lesion) caused by dermatomyositis (aetiology).

Questions

What investigations would you like to do?

• Estimation of serum creatine kinase (also known as creatine phosphokinase) levels (mirrors disease activity)

• Electromyography shows myopathic changes (spontaneous fibrillation, salvos of repetitive potentials, and short duration of polyphasic potentials of low amplitude)

• Muscle biopsy (will show necrosis and phagocytosis of muscle fibres, and interstitial and perivascular infiltration of inflammatory cells)

• MRI and MR spectroscopy of affected tissue may show abnormal signals in striated muscle and abnormalities of muscle metabolism.

In which other conditions is there proximal muscle weakness with high serum creatine kinase levels?

It may be caused by drugs such as lovastatin, chloroquine and colchicine, especially in patients on chronic haemodialysis. (Remember that steroids cause proximal muscle weakness with normal serum creatine kinase levels.)

How would you treat such patients?

• Most patients respond to steroids; prednisolone is the first-line drug for the empirical treatment of polymyositis and dermatomyositis.

• Resistant dermatomyositis may benefit from methotrexate, azathioprine and high-dose intravenous immunoglobulin.

• Those with an underlying neoplasm may see the dermatomyositis remit after treatment of the tumour.

Advanced-level questions

How would you classify polymyositis–dermatomyositis?

The classification of Bohan et al. (Medicine 1977;56:255) is into five groups:

I: primary idiopathic polymyositis

II: primary idiopathic dermatomyositis

III: dermatomyositis (or polymyositis) associated with neoplasia (Mayo Clin Proc 1986;61:645)

IV: childhood dermatomyositis (or polymyositis) associated with vasculitis

V: polymyositis (or dermatomyositis) with associated collagen vascular disease.

Mention a few disorders associated with myositis

Sarcoid myositis, focal nodular myositis, infectious polymyositis (Lyme disease, toxoplasma), inclusion body myositis, eosinophilic myositis.

What do you know about inclusion body polymyositis?

Inclusion-body myositis usually occurs in men >50 years of age. It is characterized by indolent, progressive proximal muscle weakness, which may be asymmetric, that eventually also involves distal muscles. Both myopathic and neuropathic changes can be seen on electromyography studies. Muscle biopsy reveals mononuclear infiltrates and vacuoles in the muscle cells that contain inclusion bodies. Inclusion body myositis often responds poorly to conventional therapy with steroids.

What do you understand by the term overlap syndrome?

Overlap syndrome indicates that characteristics of two different disorders are common to both. Dermatomyositis overlaps with systemic sclerosis and mixed connective tissue disease. Specific signs of systemic sclerosis and mixed connective tissue disease, such as sclerotic thickening of the dermis, contractures, oesophageal hypomotility, microangiopathy and calcium deposits, are present in dermatomyositis. Patients with the overlap syndrome of dermatomyositis and systemic sclerosis may have a specific anti-nuclear autoantibody, anti-PM/Scl, directed against a nucleolar protein complex.

Further reading

Dalakas MC. Polymyositis, dermatomyositis, and inclusion-body myositis. N Engl J Med. 1993;325:1487. (review)

Heinrich Adolf Gottron (1890–1974), a German dermatologist.

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