Table 1.

Differential diagnosis of nail psoriasis and onychomycosis

	Psoriasis	Onychomycosis
Frequency	High, commonest dermatosis with nail involvement	Very high: up to 30–40% of all nail disorders
Course	Chronic, often recurrent	Chronic, often progressive
Symptoms	Usually cosmetically and functionally embarrassing	Embarrassing, sometimes pain
Signs	Variable depending on nail structure involved	Variable, depending on severity and type of onychomycosis as well as pathogenic agent
Pits	Very common, regular in size and shape	Rare, irregular
Onycholysis	Common	Common
Discoloration	None to yellow	Yellow to brown
Spores and hyphae	Rarely spores	Very frequent
Transverse furrows	Rare	Rare
Skin lesions elsewhere	Very common	Often tinea pedum/manuum
Trauma	May be induced by Köbner phenomenon	Important predisposing factor
Heredity	Strong hereditary component, particularly in juvenile onset psoriasis	Autosomal dominant susceptibility to develop onychomycosis

Note: Copyright © 2009. Haneke E. Adapted from Haneke E. Non infectious inflammatory disorders of the nail apparatus. J Dtsch Dermatol Ges. 2009;7:787–797.¹⁰ Data from Haneke E.¹