Pityriasis Rubra Pilaris is another rare relapsing eruption, the pathogeny of which is unknown, but there are no special indications for any particular diet.
Psoriasis again, a recurrent eruption of daily observation, has a very obscure etiology, and it is consequently in obstinate cases that all sorts of diet and spa treatment are tried. Its parasitic origin is unproved. It has been thought to be a local disease of the skin which may be inherited. Many observers consider it symptomatic of a neurosis, but most frequently of some dyscrasia. The fact is psoriasis seems to be a reaction predisposed to of due to many kinds of causes, and consequently we meet with it in all sorts and conditions of people, whether apparently healthy and even robust, or rheumatic and gouty, alcoholic, plethoric, obese, and what not. The complication by trophic joint changes in a proportion of old-standing cases suggests a toxaemia, but perhaps not for all cases. Apart from the exciting cause or causes of psoriasis we may note the effect of constitutional states on it, for a fever may clear it off for a. time. The excessive use of alcohol makes it incurable, and the demand on a woman's strength, when suckling, has a marked effect in making a psoriasis intractable or causing it to evolve-.
The upshot of all this is that, as in other reactions, a most careful investigation must be made into the constitution of the patient, the functioning of the organs, the habits and mode of life, and anything that is wrong should be corrected as far as possible. The patient should understand that any disturbance of the health will probably "discover" the eruption. The diverse states of health, such as various metabolic disturbances, which may be associated with this psoriasis reaction, explains the benefit sometimes derived from a course at various spas and from strict dieting, such as is carried out at various German health institutes. In presence of a case of psoriasis then, it is desirable to prescribe a diet in relation to any improper feeding or any disordered condition present. But, although we have no proof that any particular diet is a cause of psoriasis, some dermatologists as a routine treatment recommend an absolutely vegetarian diet; eggs, fish and pastry are forbidden, sweets limited, milk not taken with meals, and often coffee and tea interdicted. In severe cases, especially with trophic bone changes, it is certainly expedient to judiciously experiment with a strict vegetarian or lacto-vegetarian, or Salisbury treatment, as most favourable results have unquestionably resulted on occasion.