Keratosis follicularis (Darier’s disease)
This rare condition is inherited as an autosomal dominant trait. Fertility tends to be low and many cases represent new mutations. The abnormal gene (on chromosome 12q23-q24.1) encodes for a molecule important in a signalling pathway that regulates cell– cell adhesion in the epidermis.
The first signs usually appear in the mid-teens, some-times after overexposure to sunlight. The characteristic lesions are small pink or brownish papules with a greasy scale (Fig. 4.3). These coalesce into warty plaques in a ‘seborrhoeic’ distribution (Fig. 4.4). Early lesions are often seen on the sternal and interscapular areas, and behind the ears. The severity of the condition varies greatly from person to person: sometimes the skin is widely affected. The abnormalities remain for life, often causing much embarrassment and discomfort.
Other changes include lesions looking like plane warts on the backs of the hands, punctate keratoses or pits on the palms and soles, cobblestone-like changes in the mouth, and a distinctive nail dystrophy in which white or pinkish lines or ridges run longitudinally to the free edge of the nail where they end in triangular nicks (Fig. 4.5).
Some patients are stunted. Personality disorders, including antisocial behaviour, are seen more often than would be expected by chance. An impairment of delayed hypersensitivity may be the basis for a tendency to develop widespread herpes simplex and bacterial infections. Bacterial overgrowth is respons-ible for the unpleasant smell of some severely affected patients.
The distribution of the lesions may be similar to that of seborrhoeic eczema, but this lacks the warty papules of Darier’s disease. The distribution differs from that of acanthosis nigricans (mainly flexural) and of keratosis pilaris (favours the outer upper arms and thighs). Other forms of folliculitis and Grover’s disease can also cause confusion.
The diagnosis should be confirmed by a skin biopsy, which will show characteristic clefts in the epidermis, and dyskeratotic cells.
Severe and disabling disease can be dramatically allevi-ated by long-term acitretin. Milder cases need only topical keratolytics, such as salicylic acid, and the control of local infection.