pityriasis

A dermatosis marked by branny desquamation. [G. fr. pityron, bran, dandruff]

- p. alba patchy hypopigmentation of the skin resulting from mild dermatitis.

- p. alba atrophicans a scaling condition of the skin followed by atrophy.

- p. capitis SYN: dandruff.

- p. circinata SYN: p. rosea.

- p. lichenoides a self-limited skin disorder of children and adults, usually divided into p. lichenoides et varioliformis acuta and p. lichenoides chronica. SYN: parapsoriasis guttata.

- p. lichenoides et varioliformis acuta (PLEVA) an acute dermatitis affecting children and young adults that runs a relatively mild course and is self-limited, although persistence of lesions and recurrence of attacks are not uncommon; vesicles, papules, and crusted lesions eventually produce smallpox-like scars. SYN: Mucha-Habermann disease, parapsoriasis lichenoides et varioliformis acuta, parapsoriasis varioliformis.

- p. linguae SYN: geographic tongue.

- p. maculata SYN: p. rosea.

- p. nigra SYN: tinea nigra.

- p. rosea a self-limited eruption of macules or papules involving the trunk and, less frequently, extremities, scalp, and face; the lesions are usually oval and follow the crease lines of the skin; occurs most commonly in children and young adults and is frequently preceded by a single larger scaling lesion known as the herald patch. SYN: p. circinata, p. maculata.

- p. rubra pilaris an uncommon chronic pruritic eruption of the hair follicles, which become firm, red, surmounted with a horny plug, and often confluent to form scaly plaques; it is most conspicuously noted on the dorsa of the fingers and on the elbows and knees and is associated with erythema, thickening of the palms and soles, and opaque thickening of the nails.

- p. versicolor SYN: tinea versicolor.

* * *

pit·y·ri·a·sis .pit-ə-'rī-ə-səs n, pl -a·ses -.sēz

1) any of several skin diseases marked by the formation and desquamation of fine scales

2) a disease of domestic animals marked by dry epithelial scales or scurf due to alteration of the function of the sebaceous glands and possibly associated with digestive disorders

* * *

n.

(originally) any of a group of skin diseases typified by the development of fine branlike scales. The term is now used only with a modifying adjective. Pityriasis alba is a common condition in children in which pale scaly patches occur on the face; it may be related to atopic eczema. Pityriasis rosea is a common skin rash, believed to be viral in origin, that starts with a single patch (a herald patch) on the trunk and is followed by an eruption of oval pink scaly macule. The spots are often aligned along the ribs. The rash clears completely in about eight weeks. Pityriasis versicolor is a common chronic infection of the skin caused by the fungus Pityrosporum, which is a normal inhabitant of the scalp. In susceptible people it changes to a pathogenic form called Malassezia furfur and produces a persistent depigmented scaly rash on the trunk. Treatment with selenium sulphide (Selsun) shampoo or with oral itraconazole readily kills the organism but the skin may take months to regain its normal colour. See also dandruff.

* * *

pit·y·ri·a·sis (pit″ĭ-riґə-sis) [Gr. pityron bran + -iasis] any of various skin diseases characterized by fine, branny scales.