Juvenile Dermatomyositis (JDM): Causes, Symptoms, Diagnosis, and Treatment

What is Juvenile Dermatomyositis?

• It is the most common inflammatory myositis in children. Incidence of JDM worldwide: 3 cases/1 million children/year. The peak age at the onset of the disease is around 4–10 years.
• Females > Males (2:1)
• Increased familial association with another autoimmune disease

What Is The Cause And Development Of Juvenile Dermatomyositis? 

Complex etiopathogenesis, multifactorial

Immunogenic Susceptibility

• Trigger factors
• Role of maternal microchimerism: Maternal cells appear in a postnatal child and can happen in utero, during childbirth, or during lactation.

Genetic Predisposition

• HLA with increased risk: B8, DRB1 0301, DQA1 0501 & DQA1 0301
• Polymorphism in TNF alpha promoter region & VNTRs in IL-1R antagonism

Role of Maternal Microchimerism: 

• Maternal cells in children may contain antigens (not themselves), can produce GVHD, or induce autoimmune phenomena leading to disease.

Infectious Triggers in JDM

• History of preceding infection for the last 3 months before JDM onset.
• Two-thirds of the cases are reported to be upper respiratory infections, and one-third is a gastrointestinal infection.
• Agents: Group A streptococcus, enteroviruses, Parvo B19, and rarely mycoplasma are common agents.

Also read: Allergic Rhinitis in Children: Symptoms, Causes, Diagnosis & Treatment 

Pathogenesis

• Genetic predisposition & maternal microchimerism in a 4-10 year old child, there is an infectious trigger, causing activation of
  • type 1 IFN pathway, leading to the over-activation of MHC
  • type 1 antigen and release of inflammatory cytokines.

• Increased adhesion molecules Increased IL-1, IL-6 → increased inflammation in muscle cells.
• Increased vWF, MCP & IL-10 inducible protein (IL-10 IP)
• IL-10-inducible proteins have pro-inflammatory effects
• The number of T cells, natural killer cells, and plasmacytoid dendritic cells has increased.

Clinical Features of JDM 

• Dermatological manifestations: 85-100%
  • Is symptom in 50% Rash
  • 25% rash comes with myopathy
• Heliotrope rash: Violet-pink discoloration, present on eyelids +/- periorbital edema

• Photosensitive rash occurs on photo-exposed neck and upper back areas in erythematous form. Also known as shawl sign.

• Malar rash/erythema on the face: involves nasolabial folds
• Gottron papules: atrophic or hypertrophic papules or patches seen on knuckles (PIP/DIP), elbow, knee, tarsal joint.

• Mechanic hands: scaly plaques or rash on palm/soles/fingers (esp. Along flexor tendons)
  • Strongly associated with anti-Jo-1 antibodies

Myositis: insidious onset, gradually progressive, proximal myopathy (shoulder & hip girdle)

• Initially: lethargy
• Later: inability to comb hair, inability to climb stairs
• Gower sign positive
• Associated with muscle tenderness in > 50% cases
  • Rarely, involvement of esophageal muscles leading to dysphagia, increased risk of aspiration
  • Respiratory muscle involvement: progressive respiratory paralysis.

Other features

• Fever
• Raynaud's phenomenon
• Periungual capillary changes
• Calcinosis
• Lipodystrophy
• Arthralgia & arthritis
• Joint contractures
• Restrictive lung disease is also seen

Also read: Abdominal Tuberculosis in Children: Symptoms, Diagnosis & Treatment

Variant of Juvenile Dermatomyositis

Amyopathic Juvenile Dermatomyositis—Dermatomyositis Sine Myositis

Prominent dermatological features but no/clinically silent myositis

Diagnosis Test

• Class rash: Heliotrope rash of the eyelids Gottron papules
• Weakness: Symmetric Proximal
• Muscle enzyme elevation ( ³1) : Creatine kinase Aspartate transaminase Lactate dehydrogenase Aldolase
• Electromyographic changes: Short, Small polyphasic, Motor unit potentials, Fibrillations, Positive sharp wave, Insertional irritability, Bizarre, high frequency, Repetitive discharges
• Muscle biopsy: Necrosis Inflammation

Key Points Related To Investigations In Juvenile Dermatomyositis

• AST elevation is seen before other muscle enzyme rise in Juvenile dermatomyositis
• ESR is usually normal and RF is negative
• ANA is + in > 80% cases

Autoantibodies In Juvenile Dermatomyositis

Myositis-Associated Antibodies (MAAS)

• SS-A
• SS-B
• Anti-Smith Antigen
• Anti-RNP
• Anti-dsDNA

Myositis-Associated Antibodies (MSAs)

• Anti-Jo-1
• Anti-Mi-2
• Anti-p155/140 (Anti - TIF-1g)
• Anti-NXP2 (Anti-MJ)
• Anti-MDA5 

Specific Associations of MSAs

• Anti-p155/140 (anti-TIF-1g) is seen in 23–30% of children with JDM. Associated with photosensitive rashes, ulceration, and lipodystrophy.
• Anti-MJ (Anti-NXP2) is seen in 12–23% of children with JDM. Associated with cramps, muscle atrophy, contractures, and dysphonia.
• Anti-MDA5 are seen in 7–33% of children with JDM—associated with ILD
• Anti-Jo-1 associated with mechanic hands

Role of other investigations

• T2-weighted MRI is useful to identify sites of muscle biopsy
• Contrast swallow study may be done in suspected palatal dysfunction and risk of aspiration
• PFT: Restrictive lung disease; reduced DLCO may be seen in fibrosis

Also read: Fetal Assessment: Key Evaluations & Prenatal Diagnosis 

Complications in Juvenile dermatomyositis 

• Risk of aspiration: Associated with either esophageal or palatal palsy
• Respiratory failure
• GIT vasculitis: colicky abdominal pain +/- occult blood loss.
  • Often diffuse in nature, the role of surgical management
  • Increased risk of massive bleeding & GIT perforation
• Cardiac involvement: Pericarditis or myocarditis → systolic & diastolic dysfunction
• ILD
• Calcinosis cutis: in 40% of patients, risk is increased in prolonged disease.
  • Calcium phosphate (hydroxyapatite) crystals are deposited in the skin, subcutaneous tissue, & muscles.
  • Ulcerative skin lesions: shows crystals in discharge
  • Increased risk of developing cellulitis
  • If in proximity to bone can produce osteomyelitis
  • The risk is particularly high in JDM patients with TNF-alpha genetic polymorphism.
• Lipodystrophy: in 10-40%
  • Loss of fat on face & buttock region
  • Associated with: PCOS, Metabolic syndrome
  • Insulin resistance, acanthosis nigricans, obesity with dyslipidemia
• Side effects related to steroid toxicity:
  • Cushing's syndrome: HTN, cushingoid facies, posterior lenticular opacities, peptic ulcers, rickets, and steroid-related psychosis.

Treatment of Juvenile Dermatomyositis

• Mainstay → Steroids ~ (> 50-70%)

Oral Prednisolone (2 mg/kg/day)

↓ slow tapering

Over 1 year

• Severe myositis esoph/response resp mc inv. → I.V. methylprednisolone (30 mg/kg/d) x 3 days → Switch to oral prednisolone
• Steroid toxicity/less response → Steroid sparing agents (Methotrexate → 15 mg/m2/week S.C)
• Some → Steroids + Methotrexate: Effective where monotherapy has failed.
• Hydroxychloroquine
  • Orally 4-6 mg/kg/day
  • Maintenance agent → Good add-on effect
• Cutaneous toxicity / hemolysis in G6PD individual
• Rituximab
• IVIG → Salvage → (2g/kg infusion every 2 weekly) x 3 doses, followed by every 4 monthly

Supportive Therapy

• Physiotherapy and Occupational therapy
• Feeding → Risk of asp → Gastrostomy or NG Tube feeding
• Sun protection: → Cover/use sunscreens with SP (SPF 30 or more)
• Calcium and Vitamin D supplementation: All

Also read: Image Based Questions On Musculoskeletal  

Important Points

• Respiratory muscle weakness causing respiratory failure in JDM includes no retraction and no hypoxemia; instead, hypercarbia is a clue.
• Incidence of JDM worldwide: 3 cases/1 million children/year.
• Juvenile dermatomyositis is the most common inflammatory myositis in children.
• History of preceding infection for the last 3 months before JDM onset.
• Two-thirds of the cases are reported to be upper respiratory infections, and one-third is a gastrointestinal infection.
• Agents: Group A streptococcus, enteroviruses, Parvo B19, and rarely mycoplasma are common agents.

Hope you found this blog helpful for your NEET SS Pediatrics Rheumatology and Vasculitis preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.