Twenty-five year-old female with sudden onset itchy skin eruption over her upper back and chest three weeks after starting a ketogenic diet

ABSTRACT

Prurigo pigmentosa is a rare pruritic inflammatory dermatosis with a unique staged clinicopathological presentation. It was first reported by Nagashima in 1971, and recently, more cases have been reported We introduce a case of a young Saudi female who developed biopsy proved prurigo pigmentosa after she followed strict ketogenic diet. Her condition resolved after she resumed a regular diet.

INTRODUCTION

An otherwise healthy 25-year-old female presented to the dermatology clinic because of sudden onset itchy skin eruption over her upper back and chest. She noticed this rash three weeks after starting a carbohydrate-restricted ketogenic diet. Initially, she visited a general practitioner who prescribed a topical antibiotic and antifungal agents without improvement. She came to the dermatology clinic because of skin hyperpigmentation over the upper back and upper chest.

On examination, there were multiple erythematous crusted papules and few intact vesicles over the upper chest and upper back. We prescribed clobetasol propionate ointment twice per day for two weeks. On a follow-up visit two weeks later she had post-inflammatory hyperpigmentation on her upper chest and back. The patient was reassured and given an appointment for two months later. After a one month she returned with the original presentation at the general practitioner after she had restarted her carbohydrate-restricted diet. On examination, there were multiple well-defined erythematous confluent papules and plaques with tiny vesicles over her upper back and chest (Figure 1). Our plan was to take two punch skin biopsies; one lesional biopsy and another perilesional biopsy for histopathology and immunofluorescence respectively. Histopathology revealed a basket weave stratum corneum. The epidermis showed a moderate amount of spongiosis with intraepidermal vesiculation and some neutrophils. In the superficial dermis, there was perivascular mixed infiltrate (mainly lymphocytes with neutrophils and eosinophils). The deep dermis was unremarkable. Immunofluorescence studies for C3, IgG, IgA, IgM, and fibrinogen were negative (Figure 2). We decided to resume a regular diet and to give her follow up appointment after 2 months. She came to her follow up appointment and all of her lesions resolved leaving only multiple reticular post-inflammatory hyperpigmentation on her upper back (Figure 3).

Figure 1.

Multiple well defined erythematous confluent papules and plaques with tiny vesicles over her upper back.

Figure 2.

Histopathology slide (×400) stained with hematoxylin and eosin. A: basket weave stratum corneum. B: The epidermis shows a moderate amount of spongiosis with intraepidermal vesiculation and some neutrophils. C: In the superficial dermis, there is perivascular mixed infiltrate (mainly lymphocytes with neutrophils and eosinophils).

Figure 3.

Two months after resuming regular diet: Multiple reticular post-inflammatory hyperpigmentation on the upper back.

DISCUSSION

Prurigo pigmentosa also known as Nagashima's disease, the name given after the first dermatologist who described the condition in 1971.¹ This condition is a rare pruritic inflammatory dermatosis which has unique staged clinicopathological presentation.¹ It presents in three stages; early stage manifests as erythematous urticarial papules/plaques assuming reticular configuration. In the second stage, papulovesicular or vesicle will ensue. Late stage shows pigmented macules in reticular pattern and distributed mainly on the upper back and chest.¹ Several published studies and reports hypothesized the association between ketosis and/or diet restrictions with prurigo pigmentosa. Treatment of this condition is resumption of a balanced diet. There is also a reported role for antibiotics like doxycycline.^2,3

Prurigo pigmentosa is increasingly reported dermatological condition and its relation to ketogenic diet is mentioned in the literature.^2,3 To our knowledge this is the first prurigo pigmentosa case reported in Saudi Arabia. The purpose of reporting this case to increase the knowledge and awareness of Saudi dermatologists toward this entity, especially among young population who follow special diet regimes.

Funding Statement

None.