Review Question - QID 108589

This constellation of proximal muscle weakness and erythematous rash of the peri-orbital areas, extensor surfaces, and proximal lateral thighs is suggestive of dermatomyositis. The most specific diagnostic test is a muscle biopsy showing an inflammatory myopathy with a lymphocytic infiltrate at the periphery of the muscle fascicle (Illustration A).

Dermatomyositis is an autoimmune disorder that is 2-3 times more common in females. The classic presentation is proximal muscle weakness in the setting of a characteristic rash. The most commonly seen cutaneous features include:

1. Erythema of the eyelids (heliotrope sign; Illustration B)
2. Thickened, red, scaly plaques of the knuckles and dorsal hands (Gottron’s papules; Illustration C)
3. Erythema of the elbows and knees (Gottron’s sign; Illustration D)
4. Erythema of the upper back/chest (shawl sign; Illustration E) and other sun-exposed areas

Dermatomyositis may be associated with interstitial lung disease, presenting in this case with shortness of breath and dry crackles on lung exam. This patient should be screened for malignancy, especially colon and ovarian cancers which co-occur frequently. Prior to the most accurate test of a muscle biopsy, this patient's workup would typically include serum testing searching for elevated levels of aldolase and CPK secondary to muscle destruction and analysis for elevated anti-Jo-1 (synthetase). This patient would then be treated with steroids and other systemic immunosuppressants.

Illustration A shows a muscle biopsy with lymphocytic infiltrate that is predominantly at the periphery of the muscle fascicle consistent with the muscle inflammation seen in dermatomyositis. Illustration B shows the classic heliotrope sign with erythema of the eyelids and some extension on the malar cheeks. Illustration C shows the classic Gottron’s papules, which are thickened, red, and scaly plaques that develop over the knuckles and joints of the dorsal hand. Illustration D shows Gottron’s sign, which is erythema over the extensor surfaces, especially at the elbows and knees. Illustration E shows the shawl sign, which is characterized by erythema over the upper back and chest (areas of increased sun exposure).

Incorrect Answers:
Answer 2: A CT scan may be useful for better characterization of this patient’s lung disease and screening her for malignancy but would not aid in the diagnosis of dermatomyositis.

Answer 3: Pulmonary function tests (PFTs) would be useful in assessing the severity of lung disease in this patient but would not aid in the diagnosis of her underlying disorder. Interstitial lung disease, as seen in dermatomyositis, presents with a restrictive pattern on PFTs, resulting in decreased FEV1 and FVC but a preserved FEV1/FVC ratio > 0.7.

Answer 4: A serum anti-nuclear antibody (ANA) is a sensitive but non-specific test often used to rule out systemic lupus erythematosus (it is very unlikely to have lupus with a negative ANA). The ANA may be elevated in dermatomyositis, but would not be the best test to diagnose the disease.

Answer 5: A skin biopsy may aid in the diagnosis of dermatomyositis but a muscle biopsy is more specific. Skin biopsies may show interface dermatitis on histologic review – a finding that may be seen in both dermatomyositis and systemic lupus erythematosus.

Bullet Summary:
Dermatomyositis is an autoimmune disorder that classically presents with proximal extremity muscle weakness, characteristic rashes (Gottron’s papules, Gottron’s sign, heliotrope sign, and shawl sign), and an increased risk for internal malignancy. Proximal muscle weakness caused by inflammatory myopathy results in elevated serum aldolase and CPK levels. Muscle biopsy is the confirmatory test of choice.