Pityriasis Rubra Pilaris is initially characterized by skin lesions described as mildly itchy, sharply pointed, horn-like, brownish-red to rosy yellow- colored papules. These papules usually occur on the back of the wrists, the outside of the forearms, underarm folds, elbows, knees, backs of the hands, and fingers. When the papules grow and connect together they produce dry, scaly, rough, red plaques over large areas of the skin. Gray, brittle nails and excessive oiliness of the glands on the scalp (seborrhea) and face may also occur. Often the edge of the eyelids are turned outward (ectropion).
The specific underlying cause of Pityriasis Rubra Pilaris is unknown. Researchers indicate that the condition may be hereditary or acquired. In many cases, Pityriasis Rubra Pilaris appears to occur randomly for no known reason (sporadically). However, in some affected individuals, evidence suggests that the disorder may be inherited as an autosomal dominant trait. Human traits, including the classic genetic diseases, are the product of the interaction of two genes for that condition, one received from the father and one from the mother.
In dominant disorders, a single copy of the disease gene (received from either the mother or father) will be expressed “dominating” the other normal gene and resulting in the appearance of the disease. The risk of transmitting the disorder from affected parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child.
Some researchers suggest that Pityriasis Rubra Pilaris may result from abnormalities in vitamin A metabolism. (Metabolism refers to the chemical processes occurring in the body.) However, such research has not been definitive, necessitating further investigation.
Pityriasis Rubra Pilaris is a rare disorder that may develop during childhood or adulthood. The condition appears to occur in males and females in relatively equal numbers. Reported cases include several affected individuals in a number of multigenerational families (kindreds) as well as isolated instances of the disorder.
Pityriasis Rubra Pilaris tends to follow a natural waxing and waning course, with episodes in which there is periodic worsening (exacerbation) or cessation (remission) of symptoms. As a result, according to many researchers, it may be difficult to evaluate the effectiveness of particular therapies. However, standard therapy for the condition typically includes treatment with vitamin A or synthetic vitamin A compounds (retinoids) administered topically or by mouth (orally). Synthetic retinoids prescribed for the treatment of Pityriasis Rubra Pilaris may include isotretinoin or etretinate. In addition, in some cases, low-dose methotrexate, a medication that is often used to fight abnormal cell proliferation (antineoplastic drug), may be prescribed.
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Online Mendelian Inheritance in Man (OMIM). Victor A. McKusick, Editor; Johns Hopkins University, Last Edit Date 6/13/95. Entry Number 173200.