Granular parakeratosis (originally termed axillary granular parakeratosis) is an idiopathic, benign, nondisabling cutaneous disease that manifests with intertriginous erythematous, brown or red, scaly or keratotic papules and plaques. It presents in all age groups and has no established clinical associations.

We wanted to assess the following: (1) the incidence of granular parakeratosis in biopsy specimens; (2) the differential diagnosis submitted with specimens requisition of granular parakeratosis; and (3) variations in its histopathology.

Between July 1, 1999 and December 31, 2003, 363,343 specimens were submitted to The Ackerman Institute of Dermatopathology in New York. A computer search was done of these specimen records and cases diagnosed with granular parakeratosis were reviewed. A thickened stratum corneum with retention of keratohyalin granules was considered diagnostic of granular parakeratosis.

Eighteen of 363,343 specimens (0.005%) were diagnosed with granular parakeratosis. The diagnosis was confirmed by re-review of specimens. All lesions were located in the axillae. All patients were adults; most were women. In only one instance was the correct clinical diagnosis of granular parakeratosis submitted with a biopsy requisition of it. Granular parakeratosis is rare, if its incidence among biopsy specimens is representative of its true prevalence. The failure to include granular parakeratosis on biopsy requisition forms of granular parakeratosis specimens indicates that dermatologists are not familiar with it. Variations of the histopathology of the 18 cases occurred but did not correlate with the clinical impressions included on biopsy requisition forms.