Nail involvement can be seen in all types of psoriasis. Note the characteristic discoloration and hyperkeratosis.
Psoriasis typically appears as well-defined reddish lesions with silvery scaling papules and plaques. The elbows and sacrum are preferentially affected.
The droplike, discrete papules of guttate psoriasis are smaller than those of plaque psoriasis and may resemble secondary syphilis or pityriasis rosea.
Plaque psoriasis is characterized by dry, scaling patches. The differential diagnosis includes nummular dermatitis, parapsoriasis, subacute lupus erythematosus, pityriasis rubra pilaris, tinea corporis, squamous cell carcinoma, and lichen simplex chronicus.
Pustular psoriasis consists of tiny, sterile pustules on erythematous skin that may coalesce into lakes of pus.