Grover's disease-like patterns in early pityriasis rubra pilaris

Abstract

Dear Editors,

Pityriasis rubra pilaris (PRP) is a poorly understood dermatological condition characterized by altered keratinization and immune dysfunction.¹ Both clinical and histological diagnosis can be challenging. While acantholysis was previously described,^{2, 3} it is not regularly mentioned in textbooks of dermatopathology. Prominent acantholytic dyskeratosis is unusual and can lead to misdiagnoses.

We report the case of a 67-year-old Caucasian male who presented with scaling erythematous lesions initially localized to the head and chest. Initially, the lesions were mainly papular, clinically resembling Grover's disease (GD) with atypical features including erythematous plaques (Figure 1a). Over 3 months, they evolved into sharply demarcated erythematous, scaling plaques on the chest, back, scalp, ears and eyebrows, sparing the extremities (Figure 1b). Accompanying symptoms were moderate pruritus, burning, and skin sensitivity. Clinical differential diagnoses at this point included seborrheic dermatitis and pemphigus foliaceus. The patient received a Coronavirus (Comirnaty^®, BioNTech) and influenza vaccine 1 to 2 months before symptom onset. Comprehensive systemic screenings were negative for underlying conditions.

Multiple histological specimens at 2 and 3 months showed an uncommon picture of prominent acantholytic dyskeratosis, resembling GD or, more precisely, Darier's disease, alongside a mildly acanthotic epidermis with foci of slightly pale keratinocytes in the upper epidermis and broad parakeratosis with flaky scaling (Figure 1c–e). Direct and indirect immunofluorescence gave negative results.

Despite initial improvement with topical steroids and ketoconazole, the lesions' morphology changed over time. Upon re-assessment at the ninth month, sub-erythroderma with confluent plaques and follicular papules had developed, sparing only small areas (nappes claires) (Figure 2a–c). Plantar keratoderma became evident (Figure 2d).

At this time, multiple biopsies showed similar epidermal changes as before, but acantholysis was extremely rare and subtle (Figure 2e, f). Some samples displayed minimal inflammation accompanied by broad compact orthohyperkeratosis with follicular plugging (Figure 2g). Upon re-examination, subtle areas of so-called checkerboard parakeratosis could be found early and late in the disease. The evolving clinical presentation and histological findings culminated in the definitive diagnosis of PRP, type I.

The present case highlights the challenges of diagnosing early PRP and provides valuable insights, as multiple biopsies and clinical photographs were available to the authors throughout the patient's disease progression. While acantholytic dyskeratosis was prominent in early biopsies, acantholysis was only subtle later-on.

Acantholysis and acantholytic dyskeratosis in PRP were previously reported.^2-7 Ko, Milstone, Choi and McNiff suggested that acantholysis is more prominent when PRP begins on the trunk instead of the head and neck, and that its presence may serve as a diagnostic clue for PRP in the differential diagnosis of papulosquamous disease.³ In their case series, early PRP with acantholysis clinically mimicked pemphigus foliaceus, guttate psoriasis, secondary syphilis, subacute lupus erythematosus and pityriasis rosea.³

However, if prominent, acantholysis and acantholytic dyskeratosis may obscure the diagnosis of PRP. Data on the chronology of these findings in PRP are sparse. In two cases, acantholytic dyskeratosis and prominent acantholysis seem to have been present in an advanced phase with widespread confluent plaques and erythroderma, respectively.^{6, 8} In another case, acantholytic dyskeratosis was seen early into the disease when the clinical differential diagnosis included pityriasis rosea.⁷ In a fourth case, prominent acantholytic dyskeratosis and GD-like clinical features preceded more typical clinical and histological changes.⁴ While not clearly detailing the extent of acantholysis, Magro and Crowson² report at least two more patients who were suspected to have GD on a clinical or histologic basis early into the disease.

Additionally, some cases of GD which ostensibly developed PRP-like eruptions were reported.^{9, 10} Upon closer inspection, histologic pictures in one of these cases suggest that the foci with acantholysis during the GD-like stages were already surrounded by broad hyperkeratosis and acanthosis with pallor in the upper epidermis suggestive of PRP.⁹ The other case featured images of early individual lesions and a histology compatible with GD before a classical PRP-like eruption developed. However, involvement of almost the entire body including the dorsum of the hands and feet and persistence for 10 years are uncommon for GD during the GD-like phase.¹⁰ While collision phenomena of GD and PRP are a possibility, we believe that these latter cases could be also interpreted as GD-like PRP preceding classic erythroderma.

In summary, our findings corroborate previous reports of prominent acantholysis and acantholytic dyskeratosis during different stages of PRP. Based on our case and literature review, we speculate that prominent acantholytic dyskeratosis is more common early during the disease and may be part of a GD-like pattern both clinically and histologically. As this pattern is prone to misdiagnosis, additional histologic findings compatible with PRP or clinicopathologic correlation can be helpful.

None.