An Unusual Presentation of Lichen Planus.

Lichen planus is a chronic papulosquamous eruption of the skin, scalp, nails, and mucous membranes. "Pruritic, purple, polygonal, planar, papules, plaques" are the traditional six "P's" of lichen planus. We describe an unusual case of lichen planus presenting as cellulitis. A 64-year-old lady with a past medical history of pyoderma gangrenosum, inclusion body myositis, and chronic kidney disease presented with a two-week history of swelling, erythema, tenderness, hyperkeratotic plaques, and blisters on the medial aspect of both thighs. She had a previous history of pyoderma gangrenosum exacerbations with similar presentations; however, current lesions were different from prior presentations. We considered the differential diagnoses of bacterial cellulitis versus pyoderma gangrenosum exacerbation. Due to the difference in these lesions from previous episodes, the patient was empirically treated for bacterial cellulitis with intravenous cefepime and linezolid. The infectious diseases team was consulted and valacyclovir was added to cover for possible herpes infection, with no improvement in symptomatology. Dermatology was then consulted, and a clinical diagnosis of psoriasiform dermatitis was made. A skin biopsy was obtained and the patient was started on prednisone. There was an immediate improvement in the papules within 24 hours. The papules cleared, leaving behind violaceous flat plaques, clinically diagnosed as lichen planus. The affected area was shrinking as compared to previous examinations. The skin biopsy was reported as chronic psoriasiform dermatitis with the main differential of lichen planus. The patient was discharged home on a tapering dose of oral prednisone, topical clobetasol, and oral moxifloxacin. This case demonstrates the importance of familiarity with rare clinical subtypes as a suspicion for lichen planus. The vesiculobullous subtype of lichen planus, as seen in this patient, tends to present as blisters and cellulitis from infection of the bullae. Treatment of the infection alone is not enough and steroids are essential. This knowledge helps change management, allows for earlier improvement and better patient outcomes.