A case of giant porokeratosis with vestiges of a cornoid lamella.

We report a case of giant porokeratosis combined with ulcerative squamous cell carcinoma. In our patient, we biopsied the skin, including the edge of the skin lesion, four times until we obtained histologic proof of a cornoid lamella. After we had established the diagnosis, we totally excised the affected skin including a 10-mm safety margin, because such lesions tend to develop into skin cancer. We reconstructed the excised area using a skin graft. After the operation, we took 13 samples of skin (seven from the lower leg and six from the sole of the foot) from the edge of the main lesion, including a putative cornoid lamella. Five of the six samples from the sole and one of the seven from the lower leg were demonstrated histologically to include a cornoid lamella. Our results suggest that skin biopsies should be taken from various sites at the edge of a giant porokeratotic lesion and in particular from the prominent ridge to prove the presence of a cornoid lamella. Shallow keratin-filled invaginations and underlying squamous cells with eosinophilic cytoplasm were observed at the edge of the lesion on the lower thigh, which might suggest a diagnosis of porokeratosis with an incomplete cornoid lamella if porokeratosis was strongly suspected from the patient's clinical features. Better recognition of giant porokeratosis is required, so that an earlier diagnosis can be made and appropriate therapy initiated in a timely manner.