Multiple minute digitate hyperkeratosis (MMDH), also known as spiny hyperkeratosis, is a rare entity first described by Goldstein in 1967.

It is characterized by

• hundreds of numerous, finger-like, minute, keratotic projections,

• generalized distribution (with a propency for the upper trunk and proximal extremities, with sparing of face, palms and soles)

• non-follicular origin.

Lesions are predominantly flesh colored (but also white, yellow, brown),  and measure 1 to 5 mm in length, 3 to 2 mm in diameter. They arise from otherwise normal skin.

It may present in early adulthood with a familial autosomal dominant inheritance pattern or sporadically in late adulthood.

Histopathology shows focal, compact orthokeratotic hyperkeratotic columns arising from a tented epidermis. The granular layer is intact as the epidermis other than the hyperkeratosis. The dermis shows no major alterations.

MMDH resembles to other digitate keratotic conditions such as:

• lichen spinulosus (folllicular keratotic papules -1 to 3 mm in diameter with horny spines are typically grouped into discrete -2 to 6 cm- plaques and the age of unset is around the adolescence)

• phrynoderma (“toad skin”) (predilection for the anterolateral aspect of the thigs and posterolateral upper aspect of arms, rare in developed countries. Due to various nutritional deficiency, often but no always Vitamin A. Histopathology reveals hyperkeratosis with prominent follicular plugging)

• spiny keratoderma of the palms and soles (“music box spine”) (numerous hard, asymptomatic, tiny spicules with filiform appearance that simmetrically involve the palms and soles as well as the lateral surface of digits. Lesions are similar to the spines of an old-fashioned music box. Histopathologically indistinguishable from MMDH but exhibits a completely different -palmoplantar- distribution)

• arsenical keratosis(it affects palms and soles. Arsenic exposure may be medicinal, via drinking water or occupational. Histopathology reveals focal orthokeratotic or parakeratotic hyperkeratosis often overlying a depressed epidermis. Digitate keratoses tend to be wider than they are tall)

• postirradiation digitate keratoses(It is a nonfollicular keratosis confined to the sites of irradiation, occurring months to years after irradiation. Histopathology reveals a focal column of parakeratotic hyperkerathosis overlying an invaginated and hypogranular or agranular epidermis)

• trichodysplasia spinulosa affects predominantly the face and is considered to be a viral infection occurring in postchemotherapy immunosuppression. Histopathology shows dilated hair follicles with proiferation of the inner root sheath cells containing large trichoyaline granules.

• hyperkeratotic spicules associated with hematopoietic neoplasia (they are follicular or nonfollicular digitate keratoses of the face -nose in particular- and may involve the scalp, trunk, and limbs. Often associated with paraproteinemia, multiple myeolma, cryoglobulinemia, but may be idiopathic. Histopathology reveals focal columns of oethokeratotic or parakeratotic hyperkerathosis with omogeneous compact eosinophilic inclusions).

• filiform verrucae(they are usually seen on the face -around the lips, nares, and eyelids coomonly, but can occur anywhere)

Careful attention to distribution, patient history, and histopatholoy enables accurate diagnosis.