PEDS-10: Connective Tissue Diseases and JIA — Part 2 (Part 2 of 2)

Section 1: Juvenile Dermatomyositis and Juvenile Scleroderma

~2:21 – Juvenile Dermatomyositis and Juvenile Scleroderma

Bottom line: juvenile dermatomyositis (JDM) is the most common pediatric inflammatory myopathy. The heliotrope rash and Gottron papules are pathognomonic. Calcinosis cutis is the JDM-defining complication, driven by anti-NXP2 antibodies and made worse by undertreatment. The Bohan and Peter criteria from 1975 still anchor diagnosis. JDM does not carry the malignancy association of adult dermatomyositis, a crucial age-specific flip. Juvenile scleroderma in children is overwhelmingly localized scleroderma (linear morphea, en coup de sabre, Parry-Romberg) rather than systemic sclerosis. Methotrexate is first-line for both.

Juvenile dermatomyositis (JDM) is the most common pediatric inflammatory myopathy, with an incidence of 2 to 4 per million children per year. The clinical picture is a child who has lost the ability to climb stairs, to get up from the floor without using the Gower maneuver, and to lift the arms above the head to wash the hair, with a characteristic skin eruption that often precedes the muscle weakness by weeks. Unlike adult dermatomyositis, JDM does NOT carry an increased risk of underlying malignancy. This is one of the clean paradigm flips between adult and pediatric rheumatology, and the boards expect the resident to know it cold. The adult dermatomyositis patient warrants an age-appropriate malignancy workup at diagnosis. The pediatric patient does not. Decades of longitudinal cohort data have proven that childhood-onset disease is an isolated primary autoimmune myopathy without an occult cancer driving it.

Diagnosis still rests on the Bohan and Peter criteria published in 1975. The criteria require the characteristic skin rash plus three of four muscle features: symmetric proximal muscle weakness; elevated muscle enzymes (creatine kinase, aldolase, aspartate aminotransferase (AST), and lactate dehydrogenase (LDH)); a myopathic electromyography (EMG) pattern of short, small, polyphasic motor unit potentials with fibrillations and positive sharp waves; and a muscle biopsy showing inflammation, necrosis, and characteristic perifascicular atrophy. The perifascicular atrophy is the histologic fingerprint of JDM, distinguishing it from polymyositis and from inclusion body myositis. The skin rash is non-negotiable: without it, the patient does not have dermatomyositis even if every other criterion is met.

The hallmark skin findings are pathognomonic when present together. The heliotrope rash is a violaceous, purple-lilac discoloration of the upper eyelids, often with periorbital edema, named for the heliotrope flower. Gottron papules are erythematous or violaceous papules overlying the MCP, PIP, and distal interphalangeal (DIP) joints, knees, and elbows. The papules sit right over the bony knuckle, which is what separates JDM from systemic lupus erythematosus (SLE). In lupus the rash spares the knuckles and crosses the intervening skin; in JDM the rash sits on the knuckles. The V-sign is a photosensitive erythematous rash over the anterior chest in a V distribution. The shawl sign is the same eruption over the upper back and shoulders. Nail fold capillary changes (dilated, tortuous, and dropout capillaries on capillaroscopy) reflect the underlying vasculopathy that drives the muscle and skin damage.

The myositis-specific antibodies in JDM define clinical phenotype and prognosis, and the five tested-favorite associations earn cold memorization. Anti-NXP2 (anti-p140) is the most common antibody in JDM and the one strongly associated with severe muscle disease and calcinosis cutis. Anti-TIF1-gamma (anti-p155/140) associates with severe cutaneous disease and photosensitivity; in adults the same antibody associates with malignancy, but in children that adult association does not hold. Anti-MDA5 (anti-CADM-140) associates with rapidly progressive interstitial lung disease, amyopathic dermatomyositis, and skin ulceration. Anti-Mi-2 associates with classic dermatomyositis and the best prognosis. Anti-SRP (signal recognition particle) associates with a necrotizing myopathy phenotype and severe disease.

Calcinosis cutis is the JDM-defining late complication. The body literally deposits solid calcium crystals into the skin, subcutaneous tissue, and deep muscle fascial planes. It affects 20% to 40% of JDM patients, strongly associates with the anti-NXP2 antibody, and is particularly common when initial treatment is delayed or disease is undertreated. The deposits cause severe localized pain, joint contracture, and eventual ulceration through the skin with secondary infection. Lipodystrophy, in which the child progressively loses the subcutaneous fat layer in a symmetric pattern, is a second distinctive complication that radically alters body composition and drives severe insulin resistance.

Treatment begins with systemic corticosteroids, typically intravenous methylprednisolone pulse therapy followed by oral prednisone. Methotrexate is the first-line steroid-sparing agent, allowing prednisone taper without disease flare. Intravenous immunoglobulin (IVIG) is reserved for refractory skin disease. Hydroxychloroquine may be added for persistent cutaneous manifestations. Rehabilitation is crucial and timing-dependent: during active disease, gentle active-assisted range of motion is maintained while eccentric exercise is avoided because it can worsen muscle inflammation. As inflammation comes under control, progressive strengthening is introduced. Sun protection with photoprotective clothing and broad-spectrum sunscreen is essential because ultraviolet light drives flares. Calcinosis prevention through early aggressive immunosuppression is the best strategy. Established calcinosis can be treated with colchicine, diltiazem, aluminum hydroxide, or surgical excision for symptomatic deposits, but no medical therapy reliably dissolves the deposits once formed.

Juvenile scleroderma in children flips the adult ratio. In adults, systemic sclerosis (the visceral form) is comparatively common. In children, localized scleroderma (juvenile localized scleroderma, JLS) dominates. JLS subtypes include circumscribed (plaque) morphea, linear scleroderma (the most common pediatric form), generalized morphea, and pansclerotic morphea. The linear scleroderma of the face is called en coup de sabre, French for “stroke of the saber,” and produces a vertical depressed band on the forehead that can extend into the scalp and cause hair loss along the band. En coup de sabre may be associated with Parry-Romberg syndrome (progressive hemifacial atrophy), in which one side of the face progressively wastes. Linear scleroderma crossing a joint produces growth disturbance and contracture in the affected limb. Methotrexate is first-line systemic therapy, with corticosteroids added for active inflammation. Juvenile systemic sclerosis is rare (roughly 5% of pediatric scleroderma) and presents like adult systemic sclerosis with Raynaud phenomenon, sclerodactyly, and possible visceral involvement (interstitial lung disease, pulmonary hypertension, esophageal dysmotility, scleroderma renal crisis); treatment overlaps with adult protocols.