The diagnosis of certain patterns of psoriasis should only be made if there is good evidence for the diagnosis. Infections and other conditions may cause pseudo-psoriasis.
Pattern of Psoriasis
Requirement to Make the Diagnosis of Psoriasis
scalp
classic changes (lesions must be palpable; mild cases should show uninvolved skin separating scaly patches)
toe or nail
(other skin manifestation of psoriasis) OR ((classic changes) AND (exclusion of Candida, dermatophytes or other condition affecting the nail))
localized pustular lesions with palmar-plantar distribution
presence of other skin manifestations of psoriasis (unequivocal nail changes, plaque psoriasis, etc)
flexural
(presence of typical lesions elsewhere) OR ((classic appearance with sharply-defined margins) AND (exclusion of Candida and dermatophytes))
If the patient has eczema or a seborrheic dermatitis, then the diagnosis of any form of psoriasis requires classical findings (plaques, nail changes, etc).
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