Girl with rash and muscle weakness

THE CASE

The mother of a healthy 10-year-old girl brings her child to the office for evaluation of new onset “eczema.” The rash is asymptomatic and began on her upper eyelids, later spreading to her chest and extremities over several weeks. The child complains of difficulty riding her bicycle. 

NEXT: What's the diagnosis?

DERMCASE diagnosis: Juvenile dermatomyositis

Juvenile dermatomyositis (JDM) is a rare, systemic, inflammatory myopathy that affects children aged 18 years and younger.¹ Skin manifestations typically precede muscle weakness, and include Gottron papules (erythematous-violaceous scaly papules over the metacarpophalangeal or interphalangeal joints, elbows, and knees); shawl sign (poikiloderma over the back of the neck, upper back, and scalp); and a heliotrope rash (violaceous edematous periorbital patches). Children also present with symmetric proximal muscle weakness that may progress over a few days to weeks, often in conjunction with myalgia.² Other organs such as the gastrointestinal tract, heart, and lungs also may be affected.³

Epidemiology

Dermatomyositis can occur at any age, but usually displays a bimodal distribution, peaking in 5- to 14-year-olds and 45- to 65-year-olds. Females are twice as likely as males to be affected.² The annual incidence of JDM in the United States ranges from 2.5 to 4.1 patients per million population. The median age of onset for JDM is 7.3 years in boys and 6.8 years in girls.¹

Pathophysiology

Juvenile dermatomyositis occurs when the humoral immune system attacks muscle capillaries and arterioles. Antibodies activate C3, leading to the deposition of membrane attack complexes (C5b-9) in endomysial vasculature. The disease eventually destroys capillaries and causes muscle microinfarction.

Next: When rash and fever become an emergency

The currently held belief is that JDM occurs in a genetically susceptible child that experiences an environmental trigger such as a viral or bacterial infection, possibly in conjunction with intense exposure to ultraviolet light.¹

Differential diagnosis

The differential diagnosis for JDM includes other inflammatory myopathies such as polymyositis, noninflammatory myopathies, and other disorders of denervation or neuropathy. The skin findings may mimic atopic dermatitis, psoriasis, drug reactions, and viral exanthema.

Clinical diagnosis of JDM can be made by the presence of proximal muscle weakness and the characteristic skin rash. Elevated muscle enzymes such as creatine kinase and aldolase are useful in confirming a diagnosis. Myositis can be definitively diagnosed by biopsy, magnetic resonance imaging, or electromyography. However, biopsy is not always performed in the presence of classic skin and laboratory findings.^2,4

Histology shows perimysial and perivascular infiltrates of macrophages, B lymphocytes, and plasmacytoid dendritic cells, as well as myofiber necrosis and regeneration. Histological findings that are more specific to JDM include endomysial microangiopathy with deposits of membrane attack complexes in capillaries. Certain antibodies are associated with different prognoses in DM. The most common antibody seen in JDM is anti-NXP-2, which is associated with calcinosis. Other antibodies include anti-Mi2, anti-TIF1γ, and anti-MDA-5.⁴

Treatment/Outcome

According to the Childhood Arthritis and Rheumatology Research Alliance, the initial treatment for JDM should include a combination of high-dose oral prednisone (2 mg/kg per day) and subcutaneous methotrexate (15 mg/m²). Dietary modifications can be made to minimize prednisone toxicity. Folic acid supplementation is recommended while the patient is on methotrexate. With the use of corticosteroids, mortality in patients with JDM is less than 2%. However, joint and muscle function can be permanently affected, and dystrophic calcification even after resolution of skin and muscle disease can be a cause of serious morbidity.³

Within a few days of starting oral prednisone and applying topical steroids to her extremities, the patient noted significant resolution of her cutaneous manifestations and improvement of muscle weakness. She has been more active, and is now able to ride her bicycle.

REFERENCES

1. Sukumaran S, Palmer T, Vijayan V. Heliotrope rash and gottron papules in a child with juvenile dermatomyositis. J Pediatr. 2016;171:318.e1.

2. Esposito AC, Munhoz T, Ocanha JP, Miot HA. Syndrome in question. An Bras Dermatol. 2016;91(3):387-389.

3. Huber AM, Giannini EH, Bowyer SL, et al. Protocols for the initial treatment of moderately severe juvenile dermatomyositis: results of a Children’s Arthritis and Rheumatology Research Alliance Consensus Conference. Arthritis Care Res (Hoboken). 2010;62(2):219-225.

4. Simon JP, Marie I, Jouen F, Boyer O, Martinet J. Autoimmune myopathies: where do we stand? Front Immunol. 2016;7:234.

Ms Boozalis is a second-year medical student at Johns Hopkins University School of Medicine, Baltimore, Maryland. Dr Cohen, section editor for Dermcase, is professor of Pediatrics and Dermatology, Johns Hopkins University School of Medicine, Baltimore. The author and section editor have nothing to disclose in regard to affiliations with or financial interests in any organizations that may have an interest in any part of this article. Vignettes are based on real cases that have been modified to allow the author and section editor to focus on key teaching points. Images also may be edited or substituted for teaching purposes.