A teenage girl presents with a new rash on her face and hands for the past few months. In addition to going to school she works as a waitress and has noted that it is harder to carry heavy trays. She also has gum inflammation and is wondering if this could be related to everything else. The physician notes the heliotrope rash around her eyes (Figure 174-1) and the Gottron papules on the dorsum of her knuckles (Figure 174-2). He considers that this may be dermatomyositis and tests for proximal muscle weakness. The proximal muscles are not found to be weak on physical exam although a subsequent blood test showed a mildly elevated CK and AST. The physician uses his dermatoscope to look at the nail folds and sees many dilated capillary loops (Figure 174-3). On the oral examination, there is a marginal gingivitis and the dermatoscope shows a similar dilated capillary pattern around the tooth. A diagnosis of dermatomyositis is made. The patient was treated with prednisone and hydroxychloroquine and improves greatly. The patient was then tapered off the prednisone fully with no relapse.

Juvenile dermatomyositis is a rare, idiopathic inflammatory disease involving the striated muscles and the skin. Similar to adult cases of dermatomyositis, the disease is primarily characterized by progressive, symmetrical, proximal muscle weakness. Dermatologic manifestations may occur with or without muscular disease and include the heliotrope rash (Figures 174-1 174-4, and 174-5), “shawl sign,” and Gottron papules over the finger joints (Figures 174-4 to 174-7). Although primarily a disease of muscle and skin, juvenile dermatomyositis has a clear association with myocarditis, vasculitis, calcinosis and interstitial lung disease.¹ Unlike adult dermatomyositis, juvenile cases are much less likely to be associated with an underlying malignancy.

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  Annual incidence of 3.2 cases per 1 million population.²

  
  
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  More common in females.^1,2

  
  
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  Children tend to have better long-term prognosis and survival compared to adults with dermatomyositis.¹

  
  
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  Mortality rate in children with dermatomyositis is lower than that of adults (less than 5.0% versus 20.8%).^1,3,4

  
  
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  Peak age of disease onset is 7 years old.^5–7

  
  
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  In contrast to adult patients with dermatomyositis, juvenile cases are much less likely to have concomitant interstitial lung disease (14% of juvenile cases versus 35% to 40% of adult cases).^8,9

  
  
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  Though linked to malignancy in 12 to 32 percent of adults, malignancy is not typically seen in children with dermatomyositis (approximately 1% of cases).^1,3,10,11,12

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  Dermatomyositis is considered an autoimmune disease of unknown etiology. Environmental exposure and infectious agents may play a role in disease pathogenesis.¹

  
  
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  In children, some studies have shown a high incidence of infectious symptoms in the months prior to disease onset, although no specific pathogen has been linked to the disease.⁶

  
  
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  Dermatomyositis is a microangiopathy that affects the skin and muscle. The muscle weakness and skin manifestations are likely a result of inflammatory cell infiltrate and activation and deposition of complement, causing lysis of endomysial capillaries and muscle ischemia.¹³

  
  
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  Muscle biopsy reveals perivascular and perifascicular inflammation, focal muscle necrosis, vasculopathy, and inflammatory cell infiltrate (particularly CD4 cells, B cells, and macrophages).^1,13

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  Diagnosis includes five criteria: “definite” (typical skin findings plus any three of criteria 1 to 4 that indicate muscle inflammation), “probable” (skin findings plus two of any criteria 1 to 4), or “possible” (skin findings plus any one of criteria 1 to 4).^1,14,15

  
  
  
  
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    Proximal symmetric muscle weakness that progresses over weeks to months.

    
    
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    Elevated serum levels of muscle enzymes (CK, AST, lactate dehydrogenase [LDH] and aldolase).

    
    
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    Abnormal electromyogram (EMG) demonstrating muscle irritability.

    
    
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    Abnormal muscle biopsy with muscle necrosis or inflammatory infiltrate.

    
    
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    Skin findings—Presence of cutaneous disease characteristic of dermatomyositis. The heliotrope rash (Figures 174-1 174-4, and 174-5) and Gottron papules (Figures 174-4 to 174-7) are considered pathognomonic. Nonpathognomonic manifestations include malar erythema, and periungual and cuticular changes (Figures 174-2 and 174-3).

  
  
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  These criteria are still considered the “gold standard,” although they are old (1975) and currently under critical review because of several limitations. The criteria do not include specific autoantibodies or MRI findings.⁵

  
  
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  Dilated nailfold capillary loops (Figure 174-3) have shown promise in juvenile dermatomyositis as a marker for both skin and muscle disease activity to guide treatment. Some authors propose adding this finding to criteria for diagnosis.^16,17

Clinical Features

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  Bilateral periorbital heliotrope erythema (pathognomonic; Figures 174-1 174-4, and 174-5) and scaling violaceous papular dermatitis in a patient complaining of proximal muscle weakness points to dermatomyositis.

  
  
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  A psoriasiform scalp dermatitis may be seen in up to 25 percent and pruritus in up to 38 percent of new cases of juvenile dermatomyositis.¹⁸

  
  
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  An older child may complain of difficulty climbing stairs, rising from a seat, or combing their hair. Notably the skin manifestations may precede, follow, or present simultaneously with muscle involvement.

  
  
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  In younger children, proximal muscle weakness is often difficult for the clinician to evaluate. Signs to look for include a child not wanting to walk or who insists on being carried, hesitancy to stand up off of the floor, difficulty keeping the head up after infancy, or the “Gower sign.”¹ The “Gower sign” is typically associated with muscular dystrophy but can be seen in the proximal myopathy of dermatomyositis (see Figure 208-1).

  
  
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  Severe muscular disease may include difficulty swallowing, choking on liquids, voice changes, or even acute respiratory failure if muscles of respiration are affected.^1,19

  
  
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  Hand involvement includes abnormal nailfolds and Gottron papules. “Moth-eaten” cuticles, also called the Samitz sign, are evidenced by periungual erythema and telangiectasias (Figures 174-2 and 174-3).

  
  
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  Juvenile dermatomyositis is more often associated with vascular disease compared to adult cases. Telangiectasias (periungual and gingival) are more common in the pediatric population (Figure 174-3).¹

  
  
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  Severe vascular disease in juvenile dermatomyositis can lead to skin ulceration in up to 24 percent of pediatric cases (Figure 174-5).²⁰ Similarly, vascular disease may lead to abdominal pain, pneumatosis intestinalis, and GI hemorrhage with risk of perforation. Persistent or severe abdominal pain in a child with juvenile dermatomyositis should prompt immediate evaluation.²¹

  
  
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  Gottron papules, smooth, purple-to-red papules and plaques, are classically located over the knuckles and on the sides of fingers (Figures 174-2 174-4 174-7, and 174-8). Plaques may be present over the knuckles instead of or in addition to papules (Figure 174-7). The papules are much more evident upon presentation of juvenile-onset dermatomyositis.

  
  
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  Calcinosis of tissues is present in up to 30 percent of cases (Figure 174-6). Calcinosis is due to precipitation of calcium and phosphate in inflamed tissues, which can lead to functional disability.^5,21–23 Typically, the deposits are on the extensor surfaces of joints and pressure points of the extremities, although they may be present anywhere.²² The presence of calcinosis may be decreased if patients are treated early and aggressively.^21,24 Calcinosis can lead to ulceration, pain from nerve entrapment, and joint contractures.²¹

  
  
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  Lipodystrophy has been associated with up to 10 to 40 percent of cases of juvenile dermatomyositis. This disease complication presents with loss of visceral and subcutaneous fat accompanied by increased insulin resistance and glucose intolerance.^1,21,25