Seborrhoea, especially of the scalp, sometimes simulates psoriasis, but the patches in the former disease are ill defined, are not so marginate, and are covered with finer, looser, and fatty scales. The lesions of psoriasis are redder and more infiltrated, and will usually be found to exist also in other localities. The disease may also be mistaken for lupus erythematosus in its early stage. The involvement of the sebaceous glands in almost all cases in the latter affection, the character of the scaling, and the fact that the face is the usual locality attacked, will aid in the diagnosis. Ringworm of the general surface may also bear resemblance to psoriasis, especially to the circular form, but the parasitic disease is more superficial and more marginate, is less scaly, and runs a more acute course. In doubtful cases the microscope should always be employed to determine the question.
TREATMENT.—The disease is rebellious to treatment, sometimes even where the lesions are few and small. It must be regarded as one of the most stubborn and persistent of the inflammatory diseases of the skin, for, while many cases yield readily to either internal or external remedies, the majority will often resist the best-directed therapeutics looking toward a permanent cure. It may often be happily dissipated for the time being, but immunity from relapses is a difficult task. To relieve the patient of the lesions, and, secondly, to prevent, if possible, relapses, should be the aim. To accomplish this demands usually both external and internal treatment. Before entering upon therapeutic measures the case should be viewed from a general standpoint. The condition of the general health should be inquired into, and the cause, if possible, determined. The history of the disease in chronic cases should be learned, and, if a relapse, the behavior of the lesions on former occasions. The influence of the several well-known remedies, such as arsenic internally, and tar, chrysarobin, and the mercurials locally, should also be ascertained. Finally, the acuteness or chronicity of the attack, the activity of the process, the amount of disease present, the locality invaded, and the general circumstances of the patient and the time that can be devoted to the treatment, should all receive consideration.
Among internal remedies, arsenic and its preparations occupy the most prominent position. For the majority of cases this remedy will be found valuable, and, if administered when indicated and in suitable doses for sufficient length of time, good results may be expected. It is not indicated in every case, as is shown by the fact that sometimes, instead of relieving, it aggravates the disease. It should be used tentatively at first, with the view of determining its tolerance and effect, not only upon the skin, but on the general system and alimentary canal. It is a powerful remedy, and should always be employed with due caution. At the same time, there need be no hesitation in prescribing it, or even in employing it for a long period, if attention be directed to its effects. Toxic symptoms should never be permitted to occur. In acute stages, whether in first attacks or in relapses, where the process is active, characterized by marked redness, inflammation, and heat, it should be withheld. At these periods it usually aggravates the disease. The more chronic the process, the more useful will the remedy probably prove.
The drug is generally administered in the form of arsenious acid, liquor potassii arsenitis, and liquor sodii arsenitis. A dose of arsenious acid varies from one-fortieth to one-fifteenth of a grain thrice daily, administered in pill form. The dose of the liquor potassii arsenitis—or Fowler's solution of arsenic, as it is generally termed—varies from one to five minims three times a day, the average dose being two or three minims. It is best to begin with a small dose and gradually to increase the quantity until the maximum dose is ascertained; after which the regular dose may be instituted. Patients, it will be found, vary as to the amount they can safely and beneficially take: in most cases two or three minims continued for a length of time will prove a full dose, while in others four or five minims will be tolerated. It may be given with water, elixir of calisaya, or wine of iron. The practice of prescribing it pure, directing a certain number of drops to be taken at each dose, is objectionable; it does not ensure an accurate quantity or proper dilution, and, moreover, gives the patient unnecessary trouble. A prescription such as the following possesses practical advantages:
| Rx. | Liq. potassii arsenitis, | fluidrachm iss; |
| Elix. calisayæ, | fluidounce iv. |
M.—Sig. One teaspoonful with a wineglassful of water thrice daily, after meals. The dose here is three minims; should it prove too strong, a half teaspoonful of the mixture may be ordered. The toxic effects of arsenic should be borne in mind. Some persons are very susceptible to the remedy, half-minim or one-minim doses sometimes causing unpleasant symptoms. The usual ill effects consist of erythema of the fauces, oedema of the eyelids, injection of the conjunctivæ, watering of the eyes, pains in the head, nausea, sharp pains in the bowels, and diarrhoea, coming on within a few days or a fortnight after beginning treatment. As a rule, they pass away in a few days after ceasing the use of the remedy.
The length of time that arsenic should be given will depend upon its effects upon the general system and upon the disease. In most cases improvement is noticeable within a fortnight, though its use from one to three months is generally necessary to bring about complete recovery; and it is best to continue the medicine in small doses for a month or two longer. Arsenic is a nervine tonic. It acts as a stimulant to the skin, exerting a decided impression upon the cells of the rete mucosum; doing this, without doubt, directly through the nerves, which, as is well known, are abundantly supplied to this structure.
Phosphorus has been used by several dermatologists, but with varying results. It is liable to produce gastric disturbance, and is a disagreeable remedy. Tar, in capsule or pill form, will sometimes prove of value where arsenic and other remedies have failed. From one to three capsules, containing from three to five grains each, may be given for a dose. Carbolic acid has also been extolled by some, especially in chronic cases with slight infiltration. Anderson speaks well of it, and gives the following formula for its administration:
| Rx. | Acidi carbolici, | drachm iij; |
| Glycerinæ, | fluidounce j; | |
| Aquæ, | fluidounce v. |
M.—Sig. One teaspoonful in a large wineglassful of water before meals.