Diagnosis. It is only in the atypical cases that doubt may arise, and then it may be confounded with one of the following diseases:

Squamous eczema will generally give some history of moisture, its patches have an ill-defined border, its scales are thickest in the center, darker and less abundant than those of psoriasis, it is located in the flexures of the joints or on the flexor surfaces, and invariably itches. Both psoriasis and eczema may affect the nails, but eczema often attacks all, psoriasis only one or more, never all at once.

Seborrhea of the scalp is generally more extensive than psoriasis. If the latter extends beyond the hairline, its characteristic appearance, and other lesions on its favourite locations may usually be found. Its scales are not dirty and fatty as are those of seborrhea.

Seborrheic dermatitis of the non-hairy parts may closely resemble psoriasis, but the scales are greasy, tend to form crusts, and the affected skin is generally a yellowish red. It seldom occurs in the favorite locations of psoriasis, and a history of a primary seborrhea on a hairy surface, and its evolution, clearly establishes its nature.

Ringworm may be distinguished by a history of contagion, asymmetrical location, elevated and at first papular margin, and when on the scalp by the short, stubby hairs. The microscope will show the presence of the fungi of ringworm.

Lupus erythematosus is usually situated on the face, an uncommon site for psoriasis. It occurs generally in middle life instead of before, as is common in psoriasis. It scales are scanty, adherent and, when removed, often show the patulous opening of the sebaceous follicle. On the scalp, lupus destroys the hair and in any location leaves scars.

Lichen planus begins as flat smooth, shining, angular papules which become closely aggregated, thus forming an infiltrated patch over which there may be a scant scaliness. Moreover, it selects the flexor surfaces especially at the wrists and sides of the knees.

Lichen ruber shows acuminate papules beginning on the trunk, and the infiltration are formed in the same way as lichen planus. When generalized, the infiltration is much greater than in like cases of psoriasis, while the scaling is much less.

Pityriasis rosea is an acute disease, and rapidly spreads all over the surface of the skin. Its scales are thin, papery, easily detached, do not fully cover the reddened skin, and never pile up.

Squamous syphilids may be mistaken for psoriasis in the absence of a history of syphilitic infection because syphilis is a polymorphous affection, but it seldom occurs on the elbows or knees, and many often be seen on the mucous surfaces, where psoriasis is never seen. In secondary syphilis, the lesions are rarely large and do not spread peripherally. The scales are scanty, dirty gray in color and not freely shed, while the brownish red color of the active lesions and the fawn colored pigmentation left after the eruption subsides, with the constitutional symptoms of the disease, should aid the diagnosis. The scaly lesions of tertiary syphilis are usually few in number and not symmetrically distributed; the edge of a patch is often elevated, while the center appears depressed, and scarring and deep stains commonly follow.

Prognosis. The historically bad prognosis of psoriasis is not longer justified. Rather it may be said to be good as far as temporary relief is concerned, and to be hopeful as to a permanent cure. It is wise, however, to inaugurate treatment when the disease is still in its infancy. The younger the patient, the less chronic the disease, and the more recurrent the type, the better the prognosis.

Frederick Dearborn
Dr Frederick Myers DEARBORN (1876-1960)
American homeopath, he directed several hospitals in New York.
Professor of dermatology.
Served as Lieut. Colonel during the 1st World War.
See his book online: American homeopathy in the world war