Histologic and immunofluorescence study of cutaneous porphyrias.

We reviewed the histologic and direct immunofluorescence findings in skin biopsy specimens from 24 patients with cutaneous porphyrias. The histopathologic changes were characterized by cell-poor subepidermal bullae, festooning of dermal papillae, thickening and hyalinization of dermal blood vessel walls, dermal sclerosis, and a mild perivascular infiltration of mononuclear cells in the upper dermis. The characteristic pattern on direct immunofluorescence testing was fluorescence of thickened doughnut-like blood vessels in the upper dermis, reflecting deposition of immunoglobulins and C3, and deposition of immunoglobulins or C3 or both at the dermal-epidermal junction in most cases. These findings are characteristic but not specific for the porphyrias; they may also be observed in the pseudoporphyria syndromes and in other clinical settings. However, the immunopathologic findings are distinctive enough to be useful in differentiating the porphyrias and pseudoporphyria syndromes from other subepidermal bullous diseases such as epidermolysis bullosa acquisita and bullous pemphigoid. The most important diagnostic test in the evaluation of the cutaneous porphyrias still is measurement of porphyrins in urine, stool, and blood.