Definition. An inflammatory disease of the skin, characterized by excessive itching and by the formation of small, discrete, colorless or pale red papules, chiefly on the extensor surfaces of the extremities, beginning in infancy or early childhood and lasting for years or throughout life.
Symptoms. There are two forms, a mild variety, prurigo mitis, and a severe form, prurigo ferox, which differ only in extent and degree but rarely change from one to the other in their course.
Prurigo mitis. The disease usually commences within the first few months of life, not uncommonly starting as an urticaria. Often upon the extensor, pin- head-sized or larger discrete papules develop. At first they are the same color as the skin and are really better appreciated by touch than by sight, but the itching is so intense and constant that the papules are soon scratched assuming a pale to deep red color, or if torn, blood crusts form with other excoriations. As a natural result of the continued irritation, the skin becomes hard, dry, indurated and pigmented; there is some mealy desquamation; the natural lines of the skin are greatly exaggerated, causing fissures; the lymphatic glands, particularly of the inguinal and axillary region, become enlarged; and the real nature of the disease is obscured by secondary developments.
Prurigo ferox or agria is applied to severe types of the disease which may be widely distributed, and result in pronounced eczematous, pigmentary, ecthymatous and hypertrophic secondary changes, probably due to great neglect or extreme poverty, and hence seldom seen in this country.
Etiology and Pathology. Prurigo is chiefly found in Austria, and it is rarely that the type described by Hebra is seen in this country. Our recent large Austro-Hungarian immigration has furnished a few more cases but usually of a mild form. Boys are more subject to the disease than girls, and while it usually begins in infancy or early childhood, cases have been reported as originating between the fifteenth and thirtieth years. A case of my own started at the fifth year. Poor food, faulty hygiene and the other prerequisites of the peasant class are largely responsible. Tuberculosis has been regarded as a causative factor. The weight of evidence seems to be that it is in nature a sensomotor neurosis. Microscopically, prurigo is a chronic inflammation similar to a long standing papular eczema. The fact that urticarial lesions sometimes precede the real prurigo papules supports the contention, as does the early history of the disease (usually furnished by the patient or some member of the family) that the itching begins without an eruption, and that the condition is a neurosis.
Diagnosis. Urticarial papules may be present at the earliest stages, but a few weeks or months will clear up the diagnosis. Chronic papular eczema may rarely exhibit a few colorless papules, and may have the same sites of preference on the extensor surfaces; but there is not the same exemption of the flexures, the colorless papules do not predominate, and papular eczema seldom dates from infancy without moist lesions, crusting, etc., or long periods of intermission from the disease. Moreover, the glandular enlargements in the groins are seldom excessive, as they may be in prurigo. Ichthyosis shows a preference for the same locations, but is characterized by polygonal scales, not papules, is not attended with much itching, and if complicated with eczema, the latter is not persistent or uniformly papular. Pruritus does not exhibit a persistent eruption of papules, and though lasting a long time, does not results in a thickening of the skin as found in prurigo. Besides as a rule there are differences in age of occurrence and location. Itching caused by animal parasites can be excluded by the absence of the peculiarities of the secondary lesions.
Prognosis and Treatment. Only mild cases and those under careful treatment seem to be curable. Severe cases persist frequently for a lifetime, although some recover spontaneously about the age of puberty. All measures that tend to improve the general health such as simple nutritious food, cleanliness, rest in bed and removal to a hospital where these items and the proper local treatment may be instituted, are in order. A daily warm or hot bath either of soap and water, some alkaline like sodium bicarbonate (4 ounces to 30 gallons of water), precipitated sulphur, or potassium sulphid (4 ounces to 30 gallons of water) should be employed. This may be followed by the application of a simple oil or if the itching remains troublesome, betanaphthol (10 to 30 grains to the ounce), sulphur ( 1 dram to the ounce), the Wilkinson salve (composed of tar, sulphur and green soap), ichthyol, diachylon or carbolic acid ointments, may be employed. Although my experience in the treatment of this disease has been limited to five cases, I have seen splendid results follow the use of Alum, Arsenicum iod., Calcarea phos., Ledum, Mang. met., Rumex. Silicea, Sulphur, and Zincum met.