What is the diagnosis and treatment plan for a patient with a heliotrope rash, low-titre Antinuclear Antibody (ANA) test, and normal cancer screening, electrocardiogram (ECG), and echocardiogram results?

Diagnosis: Dermatomyositis

This patient has dermatomyositis (DM), and the presence of a heliotrope rash alone is sufficient for classification without requiring muscle biopsy, even with a low-titre ANA. 1

Diagnostic Confirmation

The heliotrope rash is a pathognomonic skin manifestation of DM that allows accurate classification under the 2017 EULAR/ACR criteria without muscle biopsy data. 1 The key diagnostic elements are:

• Heliotrope rash presence: This pathognomonic finding, even in isolation, strongly supports DM diagnosis (positive predictive value 91% when combined with Gottron's papules). 2
• Low-titre ANA: The presence of low-titre ANA (1:80 to 1:320) is common in DM and does not exclude the diagnosis. 1 ANA screening at 1:160 dilution captures most clinically significant cases while maintaining specificity. 1
• Normal cardiac workup: The normal ECG and echocardiogram effectively exclude myocardial involvement, which would be a critical prognostic factor. 1
• Negative cancer screening: This is reassuring but does not eliminate the need for ongoing surveillance, as cancer can be associated with DM in up to 21% of pure DM cases. 2

Additional Diagnostic Workup Required

Before initiating treatment, complete the following:

• Muscle enzyme assessment: Check creatine kinase (CK), AST, ALT, lactate dehydrogenase (LDH), and aldolase to evaluate muscle inflammation. 1
• Inflammatory markers: Obtain ESR and CRP. 1
• Troponin level: To definitively exclude subclinical myocardial involvement. 1
• Myositis-specific autoantibodies: Test for anti-Mi-2, anti-Jo-1, anti-SRP, anti-PL-7, anti-PL-12, anti-MJ, and anti-p155 antibodies, as these have diagnostic and prognostic significance. 1, 2 Anti-Mi-2, anti-MJ, and anti-p155 are restricted to pure DM with 100% positive predictive value. 2
• Muscle strength assessment: Document proximal muscle weakness using validated tools like manual muscle testing (MMT). 3
• Consider skin biopsy: For DM patients without muscle involvement, skin biopsy is recommended. 1

Treatment Plan

Initiate high-dose corticosteroids combined with a steroid-sparing agent immediately upon diagnostic confirmation. 3

Initial Therapy

• Prednisone 1-2 mg/kg/day orally (or pulse IV methylprednisolone for severe disease). 3, 4, 5
• Concurrent steroid-sparing agent (start simultaneously, not sequentially):
  • First-line: Methotrexate 15-20 mg/m²/week (subcutaneous administration preferred). 3, 4, 5
  • Alternatives if methotrexate contraindicated: Azathioprine or mycophenolate mofetil. 3

Tapering Strategy

• Gradually reduce corticosteroids as clinical improvement occurs, aiming for prednisone <10 mg/day. 3
• Continue methotrexate for minimum 1 year after achieving remission on low-dose steroids before considering discontinuation. 3
• If unable to taper prednisone below 10 mg/day after 3 months, escalate to additional immunosuppression. 1

Refractory Disease Management

If inadequate response after 4-6 weeks of initial therapy: 3

• Intravenous immunoglobulin (IVIG): Particularly effective for cutaneous manifestations. 3
• Rituximab: For severe refractory cases (note: may take up to 26 weeks for effect). 3
• Cyclophosphamide 500-1000 mg/m² IV monthly: For severe disease. 3
• Cyclosporine or mycophenolate mofetil: As alternative DMARDs. 3

Critical Monitoring and Follow-up

• Serial muscle enzyme monitoring: CK, ESR, CRP to assess treatment response. 1, 3
• Muscle strength assessment: Regular evaluation using validated scales (MMT or CMAS). 3
• Ongoing malignancy surveillance: Despite negative initial screening, maintain vigilance for cancer development, particularly in the first 3 years, as DM can be paraneoplastic. 2, 6 The presence of anti-Mi-2 antibodies (if positive) does not eliminate cancer risk. 6
• Cardiac monitoring: If any cardiac symptoms develop, permanently discontinue immunosuppression and urgently reassess. 1, 3

Important Caveats

• Early aggressive treatment is essential: Delayed or inadequate immunosuppression leads to worse outcomes. 7
• Do not wait for muscle enzyme elevation: Some DM patients have normal CK levels, particularly those with predominantly cutaneous disease. 2
• Distinguish pure DM from overlap myositis: The presence of concurrent heliotrope rash with other autoimmune features (anti-Jo-1, anti-PL-7, anti-PM-Scl, anti-U1RNP) suggests overlap myositis with DM features (OMDM), which has different prognosis (65% 15-year survival vs 92% for pure DM). 2
• Perifascicular atrophy is not specific: This finding can occur in both pure DM and overlap myositis, so its absence does not exclude DM. 2