Differential Diagnosis for Rash that Looks like Shingles Crossing Midline and Recurs

• Single Most Likely Diagnosis
  • Herpes Zoster (Shingles): Although shingles typically does not cross the midline, the recurrence and the description of the rash suggest this could be a variant presentation, especially if the patient has a weakened immune system or if the rash is not strictly unilateral but predominantly so.
• Other Likely Diagnoses
  • Contact Dermatitis: Could mimic shingles if the allergen or irritant causes a linear or dermatomal distribution of the rash, and it can recur if exposure to the causative agent continues.
  • Dermatomal Metastases: Rarely, metastatic disease can present with dermatomal distribution, mimicking shingles, and can recur or spread.
  • Zosteriform Eruption (Pseudozoster): A condition that clinically resembles herpes zoster but is not caused by the varicella-zoster virus. It can be due to various causes, including contact dermatitis or other viral infections.
• Do Not Miss Diagnoses
  • Lymphoma: Cutaneous T-cell lymphoma (e.g., mycosis fungoides) can present with skin lesions that might mimic shingles, and it's crucial not to miss this diagnosis due to its significant implications.
  • Leukemia Cutis: Involvement of the skin by leukemia cells can cause a wide range of skin lesions, including those that might resemble shingles.
  • Neurosyphilis: Tabes dorsalis, a form of neurosyphilis, can cause pain and skin lesions that might be confused with shingles, especially in the context of midline crossing and recurrence.
• Rare Diagnoses
  • Sjögren's Syndrome: Can cause a variety of skin manifestations, including annular or linear lesions that might be mistaken for shingles.
  • Erythema Multiforme: Although typically presents with target lesions, it can have a wide range of manifestations and might rarely be considered in the differential for a recurrent, shingles-like rash.
  • Linear IgA Disease: An autoimmune condition that can cause linear or blistering skin lesions, potentially mimicking a shingles-like rash in rare cases.