Granular Parakeratosis of the Eccrine Ostium: A Case Report

Introduction

Granular parakeratosis (GP) is an uncommon dermatological disorder due to abnormal keratinization, with an incidence of 0.005%.^1,2 The clinical presentations include brownish to erythematous papules that sometimes coalesce into plaques, mainly on the intertriginous areas.³ Because of its clinical characteristics and benign nature, GP is usually misdiagnosed, and the correct diagnosis may be delayed for up to 20 years.⁴ In this case report, we present a case of GP of the eccrine ostium, a rare type of GP, which was definitely diagnosed almost four decades after the initial presentation of the disease.

Case Presentation

A 64-year-old Thai female visited the dermatology clinic with a 4-day history of an itchy erythematous rash on her neck. She reported experiencing the same manifestations since her twenties, with a frequency of up to three to four episodes in some years. The lesions tended to be stimulated by hot climate and profuse sweating and resolved spontaneously or after the application of topical medications. Having been previously diagnosed with either eczema or folliculitis with similar presentations, she initially received topical and oral medications from a local pharmacy to manage her symptoms. However, the lesions did not improve despite a 3-day treatment with topical pimecrolimus and oral clindamycin 300 mg twice daily. She reported that her mother also suffered from the same condition but to a milder degree. The underlying conditions included hypertension, dyslipidemia, type-2 diabetes mellitus, allergic rhinitis, major depressive disorder, non-alcoholic steatohepatitis, and myasthenia gravis.

Dermatological examination revealed multiple discrete brownish spiny keratotic papules and scaly erythematous papules on the neck (Figure 1A and B). No obvious skin lesions were observed on the axillae of the patient. Histological analysis revealed a mild epidermal hyperplasia with focal mound parakeratosis. Higher magnification showed that parakeratotic corneocytes contain multiple basophilic granules, similar to keratohyalin granules. These features were prominent in the stratum corneum of the eccrine ostia (Figure 2A and B).

Figure 1 Clinical presentations: multiple erythematous to brownish spiny keratotic papules on the neck at the initial visit (A and B).

Figure 2 Histopathology: (A) mild epidermal hyperplasia with focal mound parakeratosis (hematoxylin-eosin, x100). (B) Higher magnification showed parakeratotic corneocytes with retained keratohyalin granules, which were more prominent around the eccrine ostia (hematoxylin-eosin, x400).

Based on the clinical manifestations and histopathological findings, the patient was diagnosed with GP of the eccrine ostium. She was advised to avoid excessive heat and keep her intertriginous areas dry. At the 2-week follow-up visit, the lesions significantly improved (Figure 3A and B).

Figure 3 Significant improvement of the lesions at the 2-week follow-up visit (A and B).

Discussion

First described by Northcutt in 1991, GP is a rare acquired disorder of epidermal keratinization.^2,3 It is usually found in the adult population, although children as young as 3 months of age have been reported to have such a condition.^5,6 Females are more commonly affected than men.¹ GP usually presents as erythematous to brownish hyperkeratotic papules or plaques, mainly affecting intertriginous areas. In a recent systematic review of 129 patients with GP from 60 studies, the axilla was found to be the most commonly affected area (56.5%), followed by the groins (31.8%), inter/submammary areas (10.9%), and anogenital areas (10.1%). The neck, as in our case, was affected in 7% of all cases.⁴

GP has been found to be associated with obesity, heat, sweating, friction, and topical agents such as zinc oxide, deodorants, and benzalkonium chloride.^7–9 In terms of pathogenesis, the primary defect is in the processing of profilaggrin to filaggrin during keratinocyte cornification, resulting in failure to degrade keratohyalin granules.² Altered proliferation and maturation of the epidermis are thought to be triggered and stimulated by the aforementioned factors.^10,11 GP is also reported to be associated with other dermatological and systemic conditions such as ichthyosis, atopic dermatitis, dermatomyositis, molluscum contagiosum, fungal infection, and cancers.^9,12–18

A recent report by Chirasuthat et al proposed the classification of GP into 5 types based on clinical presentations and histopathological findings. These include intertriginous GP, GP of the eccrine ostium, follicular GP, GP acanthoma, and incidental GP. As in our case, GP of the eccrine ostium usually presents with multiple brownish spiny keratotic papules on the neck with a tingling sensation when sweating. This is generally triggered by hot environments and excessive sweating. A histopathological study demonstrated parakeratotic corneocytes containing keratohyalin granules, which usually localize to the stratum corneum of the eccrine ostia.¹²

Owing to its diverse clinical presentations, GP may be misdiagnosed as other dermatological conditions, such as eczema, contact dermatitis, Darier’s disease, confluent and reticulated papillomatosis, epidermal nevus, folliculitis, or fungal infection. Moreover, routine biopsy may not be performed in such patients because of the benign nature of GP. As a result, GP is thought to be underrecognized. There is usually a delay in diagnosis, with a mean duration of 19.2 months and a range of up to 20 years from the first presentation of the condition.^4,19 In our case, the patient reported experiencing itchy erythematous lesions similar to her current presentation since the age of 25 years. A review of her dermatologic outpatient visits revealed diagnoses of either eczema or folliculitis on multiple occasions, which were subsequently treated with topical corticosteroids or antifungals. Due to multiple recurrences of her condition, a skin biopsy was eventually performed, which revealed a diagnosis of GP.

In terms of prognosis, GP is usually self-limiting and improves after discontinuation or avoidance of the triggering factors. A recent systematic review reported that the condition spontaneously resolves in 4.7% of cases.⁴ Several treatment options have been attempted with variable responses. These include topical corticosteroids, vitamin D analogues, retinoids, ammonium lactate, antifungals, oral isotretinoin, cryotherapy, and laser therapy.^2,3,20–25 Our patient’s lesions resolved spontaneously. She was prescribed topical corticosteroids when she experienced itchiness, advised to avoid excessive sweating, and was kept dry. However, it is important to note that this case report has some limitations, including relying on anecdotal evidence from a single case and lacking generalizability.

Conclusion

We present a case of granular parakeratosis of the eccrine ostium, a rare keratotic disorder, in a patient who had suffered from the condition for almost 4 decades before the correct diagnosis was confirmed. Its recurrent and benign nature often results in GP being under-recognized and misdiagnosed as other conditions such as eczema or folliculitis. This report also highlights the importance of histopathological examination, which can help distinguish GP from other dermatological disorders with similar presentations and prevent delays in establishing a correct diagnosis.