Differential diagnosis of Psoriasis
In the majority of cases, the diagnosis of psoriasis is usually easy if the above mentioned features are borne in mind. Atypical cases may create diagnostic problems.
The following conditions must be particularly considered in differential diagnosis of psoriasis:
- Syphilitic psoriasis - The history reveals an illicit exposure and the development of chancre; the rash is less scaly, and shows some degree of induration, mucous patches and lymphadenopathy. The V.D.R.L. is positive.
- Seborrhoeic dermatitis - The scalp patches are diffuse, ill-defined and moist; the hair is matted and tangled in the crust; the crusts are greasy. Body lesions affect the flexures, the sternal and inter-scapular regions.
Sebo-psoriasis is a condition in which features both of psoriasis and seborrhoeic dermatitis arc seen as indistinguishable.
- Pityriasis rosea - A short history, centripetai distribution, a herald patch and typical oval lesions with cigarette-paper-like, centrifugal scaling.
The flexural lesions must be distinguished from those in tinea cruris, intertrigo, seborrhoeic dermatitis; the nail lesions, from the lesions in tinea unguium, eczema, paronychia and syphilis; the palmar lesions. from the other causes of hyperkeratosis; the guttate variety, from lichen planus, and the erythroderma type from the other causes of erythroderma.