Laboratory Studies
The extent of examination and laboratory tests ordered in cases of minute digitate hyperkeratosis (spiny hyperkeratosis) should be guided by the history and physical examination findings. Some physicians recommend a CBC count, a comprehensive metabolic panel, and age-appropriate cancer screening for sporadic cases. Many reported associations exist, including chronic lymphocytic leukemia. However, none is proven to be beyond coincidental co-occurrence. [13]
Imaging Studies
Age- and symptom-appropriate appropriate examinations should be ordered in the workup of minute digitate hyperkeratosis (spiny hyperkeratosis). The finding of multiple minute digitate hyperkeratosis alone may be incidental. In current practice, multiple minute digitate hyperkeratosis findings do not indicate the need for specific imaging tests.
Other Tests
No other tests are needed for minute digitate hyperkeratosis (spiny hyperkeratosis).
Procedures
Skin punch or shave biopsy may be needed to diagnose and differentiate minute digitate hyperkeratosis (spiny hyperkeratosis) from other similar-appearing punctate keratoses.
Histologic Findings
Histopathology reveals compact orthokeratotic hyperkeratotic projections that may be perifollicular but overall should be a non-follicular process. This focal column of hyperkeratosis resembles a cornoid lamella. [14] Of note, some reports in the literature list parakeratosis as a finding, rather than orthokeratosis.
The granular layer appears intact and no changes are noted in the epidermis other than the hyperkeratosis. Some reports have described granular layer changes that include increased or decreased granulation, but these may be a distinct histoclinical entity. The dermis shows no major alterations.
A clinicohistologic-based classification has been proposed, although it is not yet universally established. [15] It is divided as follows:
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Type I minute digitate hyperkeratosis (spiny hyperkeratosis) (parakeratotic columns): It is referred to as type Ia if it is palmoplantar and type Ib if it is disseminated. Rather than random number assignment, it may be more clear and simple to name it using its description. For example, Ia could best be called palmoplantar parakeratotic columnar.
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Type II minute digitate hyperkeratosis (spiny hyperkeratosis) (orthokeratotic columns): It is referred to as type IIa if it is palmoplantar and type IIb if it is disseminated.
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Type III minute digitate hyperkeratosis (spiny hyperkeratosis) (porokeratotic eccrine ostial and dermal duct nevus): This type is clinically linear in presentation and histologically shows parakeratosis associated with sweat duct structures.
This proposed classification brings to light the lack of clarity in the literature on this disease process. Types I-III may be related, or they may be different entities that have somewhat similar appearances. At this point, the literature does not yet favor the use of the criteria proposed above. In fact, new criteria and algorithms are regularly proposed. [12]
Other proposed divisions include the following [16] :
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Disseminated orthokeratotic
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Disseminated parakeratotic
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Palmoplantar orthokeratotic
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Palmoplantar parakeratotic
Immunoglobulin G deposits have been noted in multiple minute digitate hyperkeratosis associated with paraproteinemia, but these lesions do not typically occur on the extremities. [17] These lesions may also be a different entity known as spicules, which is seen in myeloma patients.
The finding of hyperkeratosis has also been described in 2 manners, as either spiked/digitiform or as columns. The authors proposed a potential difference in etiology and pathologic trigger based on the difference in histology. The most probable explanation is that the spiked/digitiform type is a different process altogether and not actual multiple minute digitate hyperkeratosis.
Ultrastructural studies show smaller-than-normal keratohyalin granules. Lamellar (Odland) bodies are normal. [18] Desmosome and basement membrane density is not known to be altered but has not been studied in detail. See the image below.
Multiple minute digitate hyperkeratosis. Published with permission granted from and with copyright retained by the American Medical Association. Clark JL, Davis G, Bennett DD. Arch Dermatol. 2008 Aug;144(8):1051-6.
Staging
Staging may be needed if an associated pathology is noted, as indicated in Pathophysiology.
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Multiple minute digitate hyperkeratosis. Published with permission granted from and with copyright retained by the American Medical Association. Clark JL, Davis G, Bennett DD. Arch Dermatol. 2008 Aug;144(8):1051-6.
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Multiple minute digitate hyperkeratosis. Published with permission granted from and with copyright retained by the American Medical Association. Clark JL, Davis G, Bennett DD. Arch Dermatol. 2008 Aug;144(8):1051-6.
