This section is from the book "A Treatise On The Materia Medica And Therapeutics Of The Skin", by Henry G. Piffard. Also available from Amazon: A Treatise On The Materia Medica And Therapeutics Of The Skin.
This affection is characterized by the development of circumscribed or diffuse scaly patches, situated upon a nonor very slightly infiltrated surface, and very slightly, if at all, reddened. The scales are firm and not imbricated like those of Psoriasis, and are not, as a rule, very adherent, being easily removed by the slightest friction, but quickly replaced by the development of a fresh supply. The surface is dry and continually desquamating. The patches vary in size, and are usually circular or oval, and may appear on any part of the surface, though the affection is most frequent upon the scalp, face, and upper part of the body, and but occasionally met with lower down. It may be either acute or subacute, the former variety being most frequent in children, though sometimes occurring in adults. In this form the infiltration is more pronounced, and the color more heightened, while the tendency to epithelial proliferation is not so great. It may last a few weeks or a month or two, and then gradually return to a healthy condition; but after the scaling subsides, and the slight infiltration undergoes resolution, a little staining, most marked on patches occurring on the lower extremities, may be perceived for a short time longer.
The subacute form is characterized by less redness and infiltration than the other, but is accompanied with more abundant and decided scale formation. When it occurs on the hairy parts, as the scalp and the beard, etc., it constitutes one of the varieties of "dandruff," and its appearance is sometimes modified by the mingling of more or less sebum with the epidermis cells, dot to incressed functional activity of the sebaceous glands. At other times the sebaceous secretion is less than normal, and the white powdery scales may be almost blown off from a scalp that is even preternaturally dry. This subacute form is usually chronic, and its duration is indefinite, often lasting for months, and even years. In those oases, when occurring on the scalp, it becomes, if unchecked, an exciting cause of premature alopecia. This, however, rarely occurs until after the affection has been years in existence. 16
Pruritus is usually present to a slight degree, rarely interfering seriously with the comfort of the patient.
As a rule, little trouble need be experienced in the diagnosis of ordinary pityriasis. Typical cases can be recognized at once, but in this, as well as in many other affections, typical cases are not the only ones met with, and hence difficulties may arise. The only affections liable to be confounded with it are cases of dry and scaly eczema in the third stages, and cases of psoriasis, in which the scaly element is not very In fart there are transition forms that, judging by appearance alone, would sometimes leave us in doubt as to which name could, with the most propriety, be assigned to the case in question. Under these circumstances the history of the eruption should be taken into account. In the majority of these doubtful cases, however, it matters very little which name is given, as the treatment would be essentially the same, whether we regarded the disease as an eczema or a pityriasis. The affection could hardly be mistaken for the one known of late years by the distinctive title of Pityriasis rubra, which is a distinct disease by itself, not apparently related in any way to ordinary Pityriasis.
The prognosis in the acute forms is good, in the subacute and chronic the ultimate prognosis is good, but it often requires some months to bring them into subjection.
Pityriasis belongs to the group of affections depending on the arthritic, dartrous, or, as I prefer to term it, the Rheumic diathesis. In other words, it is merely the local manifestation of a constitutional predisposition. The special causes which lead to the development of the eruption are unknown.
In undertaking the treatment of pityriasis, the diathesis must, of course, be taken into consideration. The principles that underlie the management of this have already been fully discussed. The general hygiene of the patient, if faulty, should be corrected, and the constitutional treatment regulated by the necessities of each particular case. Oil and iron in the debilitated; quinine and nux vomica in those accompanied with neurotic phenomena; colchicum and the benzoates in the rheumatic; mercury, podophyllum, iris versicolor, or euonymus in the bilious, etc. The drugs which have appeared to me to specially influence the eruption are Arsenic, Antimony, and Sulphur. The local treatment of pityriasis usually involves the employment of stimulating alkaline applications, followed by those containing mercury and tar. The alkaline preparations most in use are green soap, soap-spirit, borax, and ammonia. In acute cases these are used for a shorter and in subacute ones for a longer period; a single thorough green-soaping being all that is advisable in some cases, while others will be benefited by repeated applications. As soon as the parts assume a dry, tense, and glistening appearance, the alkaline applications should be discontinued, and if further stimulation seems desirable an ointment containing a little tar may be employed. If less stimulation is needed, an ointment of calomel or ammoniated mercury is preferable; later, simple emollients. I have also used to advantage the oleate of mercury, the oleate of strychnia, and the essential oils of rosemary and of sage, diluted with alcohol or castor-oil.
Besides the drugs mentioned, the following may be considered: Aci-dum Sulphurosum, 11; Dulcamara, 51; Glycerine, 56; Hydrarq. Chlor. Corros., 64; Hyd. lod. Vir., 65; Hyd. Oxid-Rub., 67; Lapsana, 73; Mais Guasto, 75; Potas. Carb., 92; Rhus Tox., 99; Scabiosa, 104; and Tri-folium Pratense, 112.