Table 1.

Differential diagnosis of Darier disease: a summary box

Disease	Main clinical symptoms	Diagnostic tests
Darier disease	Skin: small and strongly corneous red-brown papules mainly in the seborrheic areas Nails: red and white longitudinal bands, subungual hyperkeratosis and V-shaped defects in the free margin of the nail Mucosal manifestation: whitish, clustered papules with central depression Secondary superinfections and malodour Itching +/-	Biopsy and histopathological examination (dyskeratosis, acantholysis)
Seborrheic dermatitis	Erythema covered with a white to yellowish oily scales in the sebum-rich areas Very common: 1–5% of the general population	Diagnosis based on clinical picture and examination
Acanthosis nigricans	Lesions are dark-coloured, hyperkeratotic, papillary eruptions which are located on the neck and in the flexural areas Often associated with diabetes mellitus, malignancy or PCOS	Laboratory tests (elevated glucose, cholesterol levels, triglycerides)
Transient acantholytic dermatosis (Grover disease)	Winter-associated exacerbations Small papulovesicular eruptions, usually on the skin of the trunk Severe itching of the skin Mainly seen in males over the age of forty	Diagnosis based on anamnesis, clinical and histopathological examination
Familial benign pemphigus (Hailey-Hailey disease)	Skin lesions of thin-walled flaccid, inflammatory plaques covered with erosions, scabs and papillary lesions Located primarily in the armpits, groins or anus Has to be differentiated with vesiculobullous type of Darier disease	Family history Clinical picture Histopathology examination
Pemphigus vegetans	Soft blisters and erosions being difficult to heal	DIF biopsy (direct immunofluorescence) Histopathology examination Pemphigus/pemphigoid antibodies