Clinical presentation and evaluation

Presenting features of children with JIIM have been reported by numerous investigators. Two of the largest descriptions have included a total of 641 patients, mostly with JDM. Their findings are summarized in Table 1 . As expected, most patients presented with weakness and rashes. However, it should be noted that a significant proportion of children were not found to be clinically weak. Many children also present with systemic features (>80% in one series) including fever, fatigue, and weight loss. Other common symptoms include muscle and joint pain, subcutaneous edema, and symptoms of pharyngeal weakness (dysphonia or dysphagia).

Given that muscle involvement is common to all forms of JIIM, many children will present with complaints of weakness or changes in physical function. However, the extent of these changes may vary from nearly imperceptible to profound. Careful assessment of muscle strength is crucial, and the possibility of JIIM should not be discounted if weakness is not immediately obvious. Weakness primarily affects the proximal (shoulder and hip girdle) and axial (mainly paraspinal and abdominal) musculature. Distal muscle weakness may be present, but it should be less prominent than the proximal muscle weakness. Otherwise, alternative diagnoses should be considered.

In the clinic, muscle strength is most commonly evaluated using confrontational manual muscle testing (MMT). An abbreviated form of MMT has recently been validated in children using 8 muscle groups. However, MMT can be challenging, due to a variety of factors. MMT requires cooperation, and may be difficult for young children. It also requires considerable experience to determine normal strength, particularly when a full-sized adult is examining a young child.

Other tools that may be helpful in assessing strength and physical function of the child with suspected JIIM are also available. The Childhood Myositis Assessment Scale (CMAS) is a 14-item, performance-based tool that assesses muscle strength, endurance, and physical function. The CMAS is validated in children with JIIM, but is probably not useful in very young children. The CMAS explicitly includes endurance assessment through the use of timed items (eg, keeping the leg raised off the examination table for a specified time). However, some clinicians have criticized the CMAS as taking too long to administer. The Children’s Health Assessment Questionnaire (CHAQ), a 30-item self-report questionnaire commonly used in childhood arthritis, has also been validated in JIIM. Both of these tools are recognized to have significant ceiling effects (relative insensitivity to change as patients approach normal strength), but are considered useful in baseline and longitudinal evaluation of JIIM patients.

Cutaneous involvement is a feature primarily of JDM and, to a lesser extent, is also common in JCTM. These features have been reviewed in an online pictorial atlas. Some features are particularly common and highly suggestive of the underlying diagnosis. Gottron papules are raised, erythematous lesions with a fine, overlying silvery scale, which are found most commonly over the metacarpophalangeal and proximal interphalangeal joints, but can also be present over the elbows, knees, toes, and medial malleoli ( Fig. 1 ). It is not uncommon for these lesions to be mistaken for psoriasis, which they can closely resemble. Erythema in the distribution of Gottron papules is also common, and is called the Gottron sign. The presence of either Gottron papules or sign should lead to consideration of JIIM.

Typical Gottron rash (both papules and sign) in a child with juvenile dermatomyositis.

The heliotrope sign is a violaceous discoloration of the upper eyelid, sometimes accompanied by fine scaling ( Fig. 2 ). Accompanying localized swelling (periorbital edema or puffiness) is also common. An accentuation of blood vessels along the upper lash line (eyeliner sign), which may persist long after other acute cutaneous features have disappeared, is also commonly seen.

Heliotrope rash in a child with juvenile dermatomyositis. Note the distribution of erythema and presence of periorbital edema.

Abnormalities of the digital nailfold capillaries are common in JIIM, particularly JDM, and are thought to reflect the underlying vasculopathy. These changes are also commonly seen in other rheumatic disorders, particularly systemic lupus erythematosus and scleroderma. In the literature, most studies have used photomicroscopy but when prominent, capillary changes can be seen without magnification ( Fig. 3 ). In the clinic, use of a hand lens or ophthalmoscope can be very helpful. When visualizing the nailfold capillaries, abnormalities to note include dilatation, tortuosity/arborization, hemorrhage, and dropout (and resulting impact on overall capillary density). The methods for nailfold capillaroscopy are well described. This assessment is valuable both in assisting with diagnosis, as many of the other illnesses under consideration will not have these changes, and in following patients. Capillary changes, particularly capillary density, have been shown to correlate well with disease activity and other clinically relevant outcomes.

Capillary changes of the digital nailbed in a child with juvenile dermatomyositis, seen without magnification.

There are several tools available for assessing skin disease in children with JIIM, including the disease activity score (DAS), the cutaneous assessment tool (CAT), the cutaneous dermatomyositis disease area and severity index (CDASI), and the dermatomyositis skin severity index (DSSI). Some attempts have been made to compare these tools, but at this time it is not clear which of these is the most useful; they are primarily useful as research tools at present.

The 2 studies of clinical features discussed previously found that 6% to 23% of children presented with skin ulcers. The presence of skin ulceration may be suggestive of medium vessel vasculitis, and should alert the examining physician to the possibility of vasculitic involvement of the bowel. This aspect is particularly important because of the potential for a catastrophic presentation with massive gastrointestinal bleeding or perforation and infectious complications. The presence of abdominal pain (particularly if severe), hematemesis, or melena should also be considered warning signs, and warrant swift investigation and intervention.

The development of cutaneous calcium deposits in children with JIIM is an important problem. The incidence of calcinosis can vary from 20% to 40%, and increases with disease duration. It may take a variety of forms, including small asymptomatic papules, larger superficial or deep masses that can be painful and functionally limiting, and platelike calcifications in the skin or fascial planes that can have a major impact on physical function. The underlying pathogenesis is not well understood, but calcinosis has been associated with delayed or inadequate therapy and persistent skin inflammation. Unfortunately, despite some anecdotal reports, there are no established treatments for calcinosis once it has formed. Surgery can be helpful, but the lesions have a tendency to recur at the surgical site. For these reasons, prevention through the provision of optimal medical care is crucial.

Lipodystrophy, which is a loss of adipose tissue, is also described in children with JIIM (mostly JDM). It may be generalized, affecting the entire body, or localized, most commonly affecting the face or a limb. When the face is affected, this results in prominence of the masseter muscles and sunken cheeks. In the extremities, loss of fat results in a more defined appearance of the muscles. Focal depressions may also be seen. The etiology is not well understood, but in some cases is associated with inflammation of the subcutaneous tissues (panniculitis). The incidence of lipodystrophy has been reported to be 10% to 40%, but the true incidence may be higher because of difficulties in recognition. Various metabolic abnormalities have been associated with lipodystrophy, including impaired glucose tolerance, hypertriglyceridemia, steatohepatitis, and menstrual irregularities with increases in serum testosterone and hypertension. The presence of lipodystrophy should lead to investigation to uncover these potentially serious problems.

Manifestations of JIIM outside the muscle and skin are less common, but may have a major impact on the disease course. In particular, involvement of the gastrointestinal tract and respiratory systems should be noted. The main concern with the bowel is the possibility of bowel vasculitis, which may present with abdominal pain, upper or lower gastrointestinal bleeding, or perforation. Bleeding, when it occurs, may be massive and is a potential cause of mortality. Perforation and associated infectious complications is also serious and may be masked by the use of corticosteroids. These complications may occur at presentation or later in the disease course. The presence of bowel symptoms is a major cause for concern and should be investigated quickly.

Interstitial lung disease is rare in children with JIIM, but is a potential cause of late mortality. As described in adults, the development of lung disease is associated with the presence of anti-tRNA synthetase antibodies. In addition, associations with other autoantibodies have been described in children. Presentation may include cough and shortness of breath, but may also be clinically silent. Unfortunately, once established, pulmonary disease in JIIM is frequently progressive, making early detection and aggressive therapy of utmost importance.

Differential diagnosis

In the child who presents with classic proximal weakness, Gottron papules, and heliotrope rash, the diagnosis of JDM is not difficult to make. However, for many children a variety of other potential diagnoses will need to be considered; these are summarized in Box 1 . For a more detailed listing of differential diagnoses, the reader is referred to Ref.

When the presentation is one of weakness or reduction in physical function, a careful examination to determine the distribution is needed. Most patients with JIIM will present with approximately symmetric weakness of the axial and proximal muscle groups. Significant asymmetry should lead to consideration of possible local causes of weakness, such as peripheral nerve problems or structural injuries. The presence of distal muscle weakness, particularly if it is similar to or greater than the corresponding proximal weakness, should lead to consideration of alternate diagnoses, such as myopathies or dystrophies. Involvement of a neuromuscular specialist early in the evaluation process is advisable.

The absence of cutaneous features in the patient presenting with weakness is also a warning signal. Although the underlying diagnosis may be JPM, this diagnosis is very rare and may be made in error in patients with other underlying muscle problems. For this reason, careful investigation is needed before committing to a diagnosis of JPM.

Measurement of serum levels of muscle enzymes (see later discussion) may also provide some guidance regarding diagnosis. While muscle enzyme levels are frequently elevated in JIIM, extreme elevations should prompt consideration of an infectious or postinfectious cause when symptoms are acute and a myopathy or dystrophy when the symptoms are more chronic.

The association of inflammatory myositis with malignancy in adults is well established. However, whether a similar association exists in children is much less clear. There have been rare cases of malignancy-associated JIIM. It is likely wise to keep this possibility in mind, particularly when there are unusual features present, such as splenomegaly or marked lymphadenopathy.

Differential diagnosis

In the child who presents with classic proximal weakness, Gottron papules, and heliotrope rash, the diagnosis of JDM is not difficult to make. However, for many children a variety of other potential diagnoses will need to be considered; these are summarized in Box 1 . For a more detailed listing of differential diagnoses, the reader is referred to Ref.

Box 1

• 
  

  Weakness With/Without Rash

  
  
  
  
  • 
    

    Juvenile idiopathic inflammatory myopathy

    
    
    
    
    • 
      

      Juvenile dermatomyositis

      
      
    • 
      

      Juvenile polymyositis

      
      
    • 
      

      Overlap myositis (including systemic lupus erythematosus, scleroderma, mixed connective tissue disease)

      
      
    • 
      

      Focal myositis

      
      
    • 
      

      Granulomatous myositis

      
      
    • 
      

      Orbital myositis

      
      
    • 
      

      Eosinophilic myositis

      
      
    • 
      

      Malignancy-associated/paraneoplastic myositis

    
    
    
    
  • 
    

    Infection-associated

    
    
    
    
    • 
      

      Viral—influenza, Coxsackie, echovirus, parvovirus, hepatitis B, human immunodeficiency virus, human T lymphotropic virus

      
      
    • 
      

      Bacterial (pyomyositis)—staphylococcal and streptococcal species most common

      
      
    • 
      

      Parasitic— Toxoplasma , Trichinella

      
      
    • 
      

      Postinfectious—influenza B

    
    

  
  
  
  
• 
  

  Weakness only (usually) ^a

  
  
  
  
  • 
    

    Muscular dystrophies—eg, Duchenne, Becker

    
    
  • 
    

    Myopathies—eg, myotubular myopathy, nemaline rod disease

    
    
  • 
    

    Myotonic disorders

    
    
  • 
    

    Metabolic myopathies—eg, glycogen storage diseases, respiratory chain defects, mitochondrial disorders

    
    
  • 
    

    Endocrine disorders—eg, thyroid, adrenal

    
    
  • 
    

    Drug induced—eg, corticosteroids, HMG-CoA reductase inhibitors

    
    
  • 
    

    Neurogenic—both congenital (eg, spinal muscular atrophy) and acquired (eg, Guillain-Barré)

    
    
  • 
    

    Neuromuscular junction—eg, myasthenia gravis

  
  
  
  
• 
  

  Rash only

  
  
  
  
  • 
    

    Amyopathic juvenile dermatomyositis

    
    
  • 
    

    Mimicking cutaneous disease (psoriasis, eczema)

  
  

^a It is possible to see some cutaneous features, although usually not classic Gottron lesions or heliotrope.

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