Prurigo pigmentosa in an African-Canadian patient: Expanding the limited literature on skin of color

Abstract

Prurigo pigmentosa is a rare inflammatory dermatosis that predominantly affects East Asian populations, with very few reported cases in individuals with darker skin tones. The condition is characterized by pruritic, erythematous papules that evolve into a distinct, net-like pattern of hyperpigmentation. Due to its rarity in non-Asian populations, prurigo pigmentosa is often underdiagnosed or misclassified as other hyperpigmented dermatoses. We present the case of a 33-year-old African-Canadian woman who developed prurigo pigmentosa following prolonged fasting, contributing to the limited literature on this condition in skin of color. This report aims to raise awareness of prurigo pigmentosa in underrepresented populations.

Introduction

Prurigo pigmentosa (PP) is a rare inflammatory skin condition first described by Nagashima in 1971. ¹ It presents as intensely itchy, red papules that later evolve into a distinct, net-like pattern of hyperpigmentation, primarily on the trunk and neck. ¹ Despite its distinct clinical appearance, PP remains significantly underreported, especially in darker skin tones or African populations. ² While its pathophysiology is still unclear, reported triggers include metabolic changes such as ketosis, fasting, diabetes mellitus, and external factors like friction and sweating. ²

PP is a very uncommon diagnosis among people of African heritage, with the majority of cases reported in young Asian women. ³ Because the inflammatory phase may not be as noticeable in darker skin, this underrepresentation in the literature raises the possibility of underrecognition or misdiagnosis with other hyperpigmented dermatoses. Identifying PP across a range of ethnic groups is necessary to ensure accurate and timely diagnosis.

This report presents a rare case of PP in an African-Canadian woman, showcasing its clinical presentation and treatment response. It highlights the importance of recognizing PP in darker skin tones and considering it in the differential diagnosis of hyperpigmented skin conditions.

Case presentation

A 33-year-old African-Canadian woman with Fitzpatrick skin type V who has no past medical history, no family history of skin disorders, and no known allergies experienced two distinct episodes of PP, both triggered by prolonged fasting. She had no recent infections or systemic illnesses at the time of either episode. She weighs 70.5 kg, takes no regular medications aside from occasional omega-3 supplements and vitamin D.

The first episode occurred in February 2024, on the third day of a 3-day water-only fast. She developed a pruritic, erythematous rash affecting the back, chest, and neck, with tingling, itching, flushing, and mild pain. She rated her pruritus as 5/10 and pain as 2/10. Symptoms worsened with clothing friction but improved with bathing. She was evaluated by a private dermatologist and was prescribed a 6-day course of 30 mg daily oral prednisone and azelaic acid gel 15% twice daily, leading to complete resolution within 2–3 days.

The second episode occurred in January 2025, again on the third day of a water-only fast. She presented to our clinic with intensely pruritic, urticated erythematous papules, and plaques on the back and upper chest (Figure 1). Given the history of prolonged fasting, the characteristic distribution, and clinical morphology of her skin lesions, a diagnosis of PP was made. She was advised to resume a normal diet and was prescribed a topical azelaic acid to address post-inflammatory hyperpigmentation (PIH) after resolution. At 3-day follow-up, her active inflammatory lesions had completely resolved with residual PIH (Figure 2).

Figure 1.

Erythematous urticated papules and plaques on the back and upper chest.

Figure 2.

Irregular, reticulated, and net-like hyperpigmented patches following the resolution of the inflammatory phase.

The patient reports a prior history of multiple episodes of intermittent fasting not lasting more than 12 h, but they were never associated with any cutaneous eruptions.

Discussion

PP is a rare inflammatory dermatosis that primarily affects young East Asian women, with significantly fewer cases reported in individuals of African descent.^1–3 The condition is characterized by pruritic, erythematous papules that evolve into a reticulated pattern of PIH. ⁴ While its pathogenesis is not fully understood, PP has been linked to metabolic changes such as ketosis, prolonged fasting, diabetes, and external factors like friction and sweating. ⁴ In addition, the rarity of this disease in non-Asian populations raises questions about potential ethnic variations in presentation and susceptibility.

In the literature, only three studies have documented PP in Black or African-American patients.^1–3 A systematic review of PP identified two Black patients. ¹ Similarly, a multi-institutional retrospective cohort study documented two additional Black patients with PP. ² Apart from these, a single published case report has described PP in an African-American woman. ³ The small number of reported cases suggests that PP may be underrecognized in this population.

Since PP is rarely diagnosed in Black or African patients, its clinical course in individuals with darker skin is not well characterized.^1–3 The erythematous phase of PP may be less apparent in darker skin, potentially delaying recognition or leading to misclassification as other hyperpigmented dermatoses such as lichen planus pigmentosus or confluent and reticulated papillomatosis. The presence of PIH, which is a more prominent sequela in darker skin tones, may further complicate diagnosis.

The patient developed two distinct episodes of PP, both occurring during prolonged fasting. Her presentation was consistent with previously reported cases, in which lesions have an acute inflammatory phase affecting the back, neck, and upper chest in a symmetric distribution and subsequent hyperpigmentation. The temporal association of prolonged fasting with the rapid resolution of symptoms upon resumption of a regular diet reinforces the documented role of metabolic changes in PP.

The limited number of reported cases highlights the need for increased awareness of PP across diverse ethnic groups, as timely recognition can help distinguish it from other pigmentary conditions with similar presentations.