"Psoriasis is often mistaken for other dermatological conditions, such as dermatitis or rashes, connective tissue disorders, mycosis fungoides, autoimmune conditions, photosensitivity, and contact dermatitis, among other things. They can be narrowed down by response to treatment clinical picture, epidemiological risk factors, family or personal history, symptoms and clinical experience of the dermatologist. A skin biopsy may also be helpful at distinguishing psoriasis from other causes. Psoriasis can occasionally be mistaken by other similar skin conditions that appear similar clinically or can be accompanied by plaque-like itchy and scaly rashes on the body as well. The differential diagnosis for psoriasis includes steroid induced rashes, mycosis fungoides, drug reactions, seborrheic dermatitis, contact dermatitis, and dermatomyositis. Connective tissue and other photo-sensitivity disorders such as systemic lupus erythematosus can present with rashes on the body, which may appear somewhere to psoriasis. Itching and skin lesions due to other causes may also confound the diagnostician and need to be ruled out. Other items on the differential include impetigo, which typically presents with gram-positive cocci in the bullous cavity, superficial candida, which will show yeast and pseudo-hifi instead, in the stratum corneum. [?] infections or superficial fungal infections, that'll show branching hyphae, and the stratum corneum, superficial folliculitis, which will typically show pustules at the follicular orfices and in the infundibulum. Pemphigus foliaceous and erythematosus, which will show acantholytic cells in the histology and direct immunofluorescence will help to distinguish this. And there will also be anti desmoglein-1 antibodies. IgA pemphigus, sub-corneal pustular dermatosis types, will typically show intercellular IgA deposits and will have antibodies against desmoglein-1. Sneddon-Wilkinson disease, which is a sub corneal pustular dermatosis, may be indistinguishable from IgA pemphigus, but will have a negative direct immunofluorescence, and pustular psoriasis, which will show spongiform pustules. Acute generalized exanthematous pustulosis will show mild spongiform postulation, less prominent than in pustular psoriasis and eosinophils. Anti-microbial pustulosis of the folds will show spongiform pustules as well. Transient neonatal pustular melanosis and acropustulosis of infancy can often be distinguished by the age group of the patient, which is typically a lot younger than a typical psoriasis patient."
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