Ultrastructure of pityriasis rubra pilaris with observations during retinoid (etretinate) treatment.

The light and electron microscopic structure of pityriasis rubra pilaris (PRP) is described in five patients. Hyperkeratosis, hypergranulosis, keratotic plugs in the follicular openings, acanthosis and focal parakeratosis were observed. A moderate perivascular infiltrate was seen in the upper dermis. Electron microscopy revealed moderately activated keratinocytes, a decreased number of tonofilaments and desmosomes, enlarged intercellular spaces, parakeratosis with lipid-like vacuoles and a large number of keratinosomes. Lymphoid cells were present in the epidermis in moderate numbers. At the dermo-epidermal junction, the basal lamina was focally split, containing gaps. Etretinate therapy produced moderate to marked clinical improvement. The histological picture improved but the typical signs of PRP, including follicular plugging, persisted. Ultrastructurally the cellular activity and the amount of hyperkeratosis and parakeratosis decreased, while increases in keratinosomes, intercellular substance, microvilli and desmosomes were observed during treatment.