Axillary granular parakeratosis
Published Web Locationhttps://doi.org/10.5070/D37059w77n
Axillary granular parakeratosis
From the Ronald O. Perelman Department of Dermatology, New York University
Monika Srivastava MD, and David Cohen MD MPH
Dermatology Online Journal 10 (3): 20
A 71-year-old man developed a pruritic axillary eruption. Histopathologic examination showed laminated orthokeratosis, parakeratosis, and hypergranulosis. There changes were consistent with a diagnosis of axillary granular parakeratosis. Axillary granular parakeratosis is an intertriginous eruption that is usually found in the axillae of middle-aged women and is characterized clinically by pruritic, erythematous, hyperkeratotic plaques and histologically by parakeratosis with retention of keratohyaline granules. Pathophysiology is thought to involve a defective profilaggrin-filaggrin pathway. Evidence-based treatment of this disorder is not available.
History.—A 71-year-old man developed a pruritic, bilateral, axillary eruption in February 2003. The patient denied the use of any new personal hygiene products. There was no involvement of other intertriginous sites. Initial treatment with oxiconazole nitrate cream and desonide cream did not result in improvement or resolution of the eruption.
Medications include allopurinol, triamterene and hydrochlorothiazide, isosorbide mononitrate, terazosin, and celecoxib. Medical history includes hypertension, arthritis, nephrolithiasis, gallbladder disease, and cutaneous squamous-cell carcinomas.
Physical examination.— In the axillary vaults, there were erythematous, keratotic papules and plaques. Fissures and erosions also were present.
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Histopathology.—There is slight epidermal hyperplasia with hypergranulosis, laminated orthokeratosis, and focal parakeratosis. There are a few dilated blood vessels in the papillary dermis and a superficial and mid-dermal perivascular infiltrate of lymphocytes and a few plasma cells. A periodic-acid-Schiff stain is negative for fungi.
Diagnosis.—Axillary granular parakeratosis.
Axillary granular parakeratosis was initially described in 1991 in four patients with an erythematous eruption in the axillae. 
Histopathologic examination showed a distinct form of parakeratosis with retention of keratohyaline granules in the stratum corneum. Since then there have been 32 additional reports. [2,3] Thirteen of these cases of granular parakeratosis occurred in sites other than the axillae, which included the groin, inframammary areas, intermammary areas, perianal areas, and the abdomen. [2,3]
Granular parakeratosis usually occurs in women, with a female-to-male ratio of 25:1. The average age is 58 years. 
Granular parakeratosis appears as erythematous or hyperpigmented, keratotic papules or plaques that are typically found in the axillae or other intertriginous areas. Scale or crust may occur, and satellite papules also may be present. Affected patients usually experience pruritus or burning.
The etiology of granular parakeratosis is unknown. One hypothesis suggested that exposure to a contactant in personal hygiene products, such as antiperspirants or deodorants, resulted in the eruption.  However, this theory does not explain the unilateral occurrence of this eruption or its location in other intertrigenous sites. [4,5] Other theories propose that multiple insults to intertriginous areas, such as mechanical irritation and humidity, lead to a protective epidermal proliferation that results in granular parakeratosis. 
The putative pathophysiological mechanism of granular parakeratosis involves a defective pathway in which profillagrin is unable to form fillagrin.  Fillagrin is essential as an adhesion matrix for keratohyaline granules during normal cornification.
Immunoelectron microscopic studies demonstrated that fillagrin was not present in the granular parakeratotic cells. Patients with granular parakeratosis exhibit a lack of degradation of keratohyaline granules and aggregation of keratin filaments. This abnormality results in the histopathologic picture of hyperkeratosis and parakeratosis with retention of keratohyaline granules.
The clinical differential diagnosis of granular parakeratosis includes Hailey-Hailey disease, pemphigus vegetans, acanthosis nigricans, inverse psoriasis, tinea infections, and intertrigo. The diagnosis is confirmed by examination of a biopsy specimen.
The treatment of granular parakeratosis includes glucocorticoids, antifungals, antibiotics, vitamin D analogues, and retinoids. Physical destruction with cryotherapy also has been described. There have been reports of spontaneous remission. [1-6]
References1. Northcutt AD, et al. Axillary granular parakeratosis. J Am Acad Dermatol 1991; 24:541.
2. Wallace CA, et al. Granular parakeratosis: a case report and literature review. J Cutan Pathol 2003; 30:332.
3. English JC, et al. Axillary granular parakeratosis. J Cutan Med Surg 2003; 7:330.
4. Webster CG, et al. Axillary granular parakeratosis: response to isotretinoin. J Am Acad Dermatol 1997; 37:789.
5. Mehregan DA, et al. Intertriginous granular parakeratosis. J Am Acad Dermatol 1998; 39:495.
6. Metze D, Rutten A. Granular parakeratosis-a unique acquired disorder of keratinization. J Cutan Pathol 1999; 26:339.
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