Differential Diagnosis for a 52-year-old Female with Specific Clinical Findings

Given the clinical presentation of a 52-year-old female with a positive dsDNA, positive ANCA at 1:640, normal C3/4 levels, facial skin lesions not responsive to retinoids, and the question of whether it is lupus, the differential diagnosis can be organized as follows:

• Single Most Likely Diagnosis

  • Systemic Lupus Erythematosus (SLE): The presence of positive dsDNA antibodies is highly suggestive of SLE. Although the ANCA positivity could suggest other diagnoses, the combination of dsDNA positivity, facial skin lesions, and the specific mention of SLE in the question makes it the most likely diagnosis. The lack of responsiveness to retinoids could be due to the underlying autoimmune nature of the condition.

• Other Likely Diagnoses

  • Granulomatosis with Polyangiitis (GPA): Given the high ANCA titer, GPA (formerly known as Wegener's granulomatosis) is a consideration, especially if there are symptoms suggestive of vasculitis or granulomatous disease. However, the presence of dsDNA antibodies and the specific skin manifestations might lean more towards SLE.
  • Mixed Connective Tissue Disease (MCTD): This condition can present with overlapping features of SLE, scleroderma, and polymyositis/dermatomyositis, and can have positive ANA and sometimes ANCA. The lack of specific symptoms like arthralgias, myalgias, or esophageal dysmotility makes this less likely but still a consideration.

• Do Not Miss Diagnoses

  • Vasculitis (e.g., Microscopic Polyangiitis, Eosinophilic Granulomatosis with Polyangiitis): These conditions can present with skin lesions and positive ANCA. Missing these diagnoses could lead to significant morbidity and mortality due to potential organ involvement.
  • Sjögren's Syndrome: Although less likely given the specific findings, Sjögren's can sometimes present with skin manifestations and positive ANA/ANCA. It's crucial not to miss this diagnosis due to its potential for extraglandular manifestations and association with lymphoma.

• Rare Diagnoses

  • Relapsing Polychondritis: This condition involves cartilaginous structures and can have skin manifestations, but it's less likely given the specific immunological findings.
  • Sarcoidosis: While sarcoidosis can present with skin lesions and sometimes positive ANA, the specific combination of dsDNA positivity and high ANCA titer makes it less likely. However, it remains a consideration in the differential diagnosis due to its potential for multi-organ involvement.

Given the clinical presentation, starting treatment for SLE seems appropriate, with careful monitoring for signs of other conditions, especially those that could be life-threatening if missed.