Post-radiation lichen planus: a case report and review of the literature.

Background: Lichen planus is a T-cell mediated inflammatory disorder of the skin and mucus membranes and is a rare complication of external beam radiation.

Case Presentation: 64 year old White male who presented to dermatology with a lesion at the lateral aspect of the right thigh. The lesion was first noted 40 years prior and had grown from 1.5 cm to 6.5 cm in the ensuing years. On examination the lesion was raised, hypopigmented, with pearly borders and central ulceration. Wide excision with lymph node dissection demonstrated invasive squamous cell carcinoma, basaloid type, with negative margins. Patient had radiation therapy of the right inguinal nodes. Patient subsequently noted a "blister" on the right upper thigh, which progressed over time to flat, polygonal, intensely pruritic lesions that covered the right lateral thigh from just distal to the hip to the distal third of the femur (Figs. 1, 2). Skin biopsy was positive for lichen planus. He was started on topical triamcinolone with salutary effects on appearance and pruritus. Fig. 1 Lichen planus, right thigh Fig. 2 Closeup, lichen planus, right thigh, demonstrating polygonal papules CONCLUSION: Once more biopsy-proven cases of post-radiation lichen planus are reported, hopefully the exact mechanism can be elucidated. This may identify risk factors and aid in treatment, with the goal of limiting radiation toxicity and palliation of symptoms that may affect the quality of daily life.