Bullous Prurigo Pigmentosa Following a Ketogenic Diet

Prurigo pigmentosa is a rare inflammatory dermatosis that was first reported in Japan in 1971. The condition is characterized by erythematous papules arranged in a reticular pattern, which typically resolve leaving behind hyperpigmentation. Although the condition is rare, it has been observed in various populations and has been associated with different triggers, including dietary changes, ketosis, diabetes mellitus, and pregnancy. This article delves into a specific case of bullous prurigo pigmentosa that developed in a young woman following a ketogenic diet, exploring the clinical presentation, diagnostic process, and management of this rare dermatological condition.

Clinical Presentation

The case involves a 21-year-old woman who presented with itchy eruptions that had been evolving over two weeks. Despite the use of topical corticosteroids, the eruptions showed no improvement. The patient had no significant past medical history or family history of dermatological conditions. On physical examination, multiple scaly erythematous papules and brownish macules were observed, coalescing into plaques and patches arranged in a reticulate pattern. These lesions were located on the chest, back, sacrum, and mons pubis. Additionally, tense vesicles were scattered on the chest, back, and sacrum.

The initial differential diagnosis included various dermatological conditions such as confluent reticulated papillomatosis, acute lupus erythematosus, and dermatitis herpetiformis. To aid in the diagnosis, direct microscopy examination of scrapings from the scaly papules on the chest was performed, which showed no evidence of fungal infection. Serum biomarkers for systemic lupus erythematosus were also within normal ranges.

Diagnostic Process

Due to the lack of a clear diagnosis during the initial visit, no specific treatment was administered. The patient returned one week later for biopsy results, by which time the eruptions had resolved spontaneously, leaving reticular pigmentation. The patient reported that she had been following a ketogenic diet for two weeks prior to the emergence of the eruptions. By the time she presented to the department, she had already returned to a normal diet that included carbohydrates.

Two skin biopsies were taken during the initial visit: one from a vesicle for regular hematoxylin and eosin staining, and another from a perilesional normal-appearing site for direct immunofluorescence. The biopsy results demonstrated focal epidermal necrosis, intraepidermal bulla with a few lymphocytes and neutrophils, and lymphocytic infiltrate in the papillary dermis. Direct immunofluorescence was negative for IgM, IgG, IgA, and C3. Based on these findings, a diagnosis of prurigo pigmentosa was made.

Etiology and Pathogenesis

The exact etiology of prurigo pigmentosa remains unclear, but several conditions have been associated with its development. These include ketosis, dietary changes, diabetes mellitus, and pregnancy. In this case, the patient had been following a ketogenic diet, which involves reducing carbohydrate intake to less than 50 grams per day while increasing the consumption of fats and proteins. This dietary change likely induced a state of ketosis, which has been previously reported to trigger prurigo pigmentosa, particularly in young women.

Bullous prurigo pigmentosa is an even rarer manifestation of the condition. It is thought to be induced by intense rubbing, which leads to extensive inflammation, intercellular and intracellular edema, basal liquefaction, and papillary dermal edema, resulting in vesiculobullous lesions. The involvement of the mons pubis in this case is particularly unusual, as the most commonly affected sites are typically the back, chest, and neck.

Management and Follow-Up

In most cases of prurigo pigmentosa, the reintroduction of carbohydrates into the diet is sufficient to resolve the condition. In this case, the patient had already returned to a normal diet by the time she presented to the department, and her eruptions resolved spontaneously without any specific treatment. Urinary examination revealed normal ketone levels on the second visit, indicating that the ketogenic state had been reversed.

The patient was followed up for 20 months, during which there was no relapse of the condition. This suggests that the dietary change was the primary trigger for the development of bullous prurigo pigmentosa in this case. However, in cases where dietary changes are insufficient to resolve the condition, oral cycling antibiotics are usually the first-line therapy.

Histopathological Findings

The histopathological findings in prurigo pigmentosa are stage-specific. In the early stages, there is a superficial perivascular neutrophil infiltrate, which is followed by a scattering of neutrophils in the dermal papillae. In this case, the biopsy demonstrated focal epidermal necrosis, intraepidermal bulla with a few lymphocytes and neutrophils, and lymphocytic infiltrate in the papillary dermis. These findings are consistent with the histopathological changes observed in bullous prurigo pigmentosa.

Differential Diagnosis

The differential diagnosis for prurigo pigmentosa includes several other dermatological conditions. Confluent reticulated papillomatosis is characterized by hyperkeratotic papules that coalesce into plaques, typically located on the trunk. Acute lupus erythematosus presents with erythematous plaques and systemic symptoms, and dermatitis herpetiformis is characterized by pruritic vesicles and papules, often associated with celiac disease. In this case, the absence of fungal infection, normal serum biomarkers for lupus, and the specific histopathological findings helped to rule out these differential diagnoses and confirm the diagnosis of prurigo pigmentosa.

Conclusion

This case highlights the rare occurrence of bullous prurigo pigmentosa following a ketogenic diet. The condition is characterized by pruritic lesions arranged in a reticulate configuration, which resolve with hyperpigmentation. The histopathological findings are stage-specific and include focal epidermal necrosis, intraepidermal bulla, and lymphocytic infiltrate in the papillary dermis. The reintroduction of carbohydrates into the diet is usually sufficient to resolve the condition, although oral cycling antibiotics may be required in some cases.

The involvement of the mons pubis in this case is particularly unusual, as the most commonly affected sites are typically the back, chest, and neck. The patient had no relapse of the condition during a 20-month follow-up period, suggesting that the dietary change was the primary trigger. This case underscores the importance of considering dietary changes as a potential trigger for prurigo pigmentosa, particularly in young women following a ketogenic diet.

doi.org/10.1097/CM9.0000000000001322

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