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Daniel Croom, MD; Thomas Barlow, DO; J. Thomas Pruritic rash on chest and back Landers, MD Department of Dermatology, Naval Medical Center San Was a recent change in diet to blame for this Diego, Calif

patient’s rash? [email protected]

DEPARTMENT EDITOR Richard P. Usatine, MD University of Texas Health a 26-year-old woman presented to our clin- was an otherwise healthy stay-at-home moth- at San Antonio ic with pruritic, hyperpigmented, symmetric er with an unremarkable medical history. The authors reported no potential conflict of interest relevant to this edematous plaques on her upper flank, chest, ●  WHAT IS YOUR DIAGNOSIS? article. and lower back (FIGURE) 3 weeks after starting The views expressed in this article a strict ketogenic (high fat/low carbohydrate) ● HOW WOULD YOU TREAT THIS are those of the authors and do not reflect the official policy or position diet for postpartum weight loss. The patient PATIENT? of the Department of the Navy, Department of Defense, or the US government. All authors are military service members. This work was prepared as part of their official duties. FIGURE Edematous, reticulated rash on upper flank and back PHOTO COURTESY OF: DANIEL CROOM, MD

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Diagnosis: often have a pale center. The lesions may occur pigmentosa anywhere on the body and generally last less We recognized that this was a case of prurigo than 24 hours. History may reveal a trigger in- pigmentosa based on the characteristic pru- cluding drugs, infection, food, or emotional ritic rash that had developed after the patient stress in up to 50% of cases.5 started a strict ketogenic diet. ❚ Irritant contact often is as- ❚ Prurigo pigmentosa is a benign, prurit- sociated with a stinging or burning sensation. ic rash that most commonly presents with ery- Irritant and allergic may thematous or hyperpigmented, symmetrically have a geometric, or “outside job,” distribu- distributed urticarial papules and plaques on tion suggestive of external contact, potential- the chest and back. Females represent approx- ly with plants, alkalis, acids, or solvents.5 imately 70% of cases with a predominant age ❚ Confluent and reticulated papillo- range of 11 to 30.1 matosis is a rare asymptomatic dermatosis While the pathophysiology remains un- of unknown etiology that presents as hy- known, the rash most often is reported in perpigmented papules on the upper trunk, association with ketogenic diets.1 Despite oc- neck, and axillae. Most patients lack associ- curring in only a fraction of patients on the ated pruritis which is in contrast to prurigo ketogenic diet, the characteristic presentation pigmentosa.6 has led to the alternative name of the “keto ❚ Pityriasis rosea is a viral exanthem that The characteristic rash” in online nutritional forums and blogs. may be associated with constitutional symp- presentation Although prurigo pigmentosa is relatively toms and often presents initially with a herald of prurigo uncommon (with an unknown incidence), patch progressing to a classic “Christmas tree” pigmentosa has primary care physicians may begin to encoun- distribution with a fine collarette of scale. It of- led to the ter the characteristic rash more frequently, ten is asymptomatic, although some cases may alternative name given the number of articles over the past be pruritic.5 of the “keto 5 years in the primary care and nutrition- rash” in online al literature highlighting the diet’s health nutritional benefits.2 The ketogenic diet is a high-fat, Treatment focuses forums. low-carbohydrate diet with preliminary evi- on dietary modification dence of improved weight loss, cardiovascu- Primary treatment includes resumption of a lar health, and glycemic control suggested by normal diet. This often leads to rapid resolu- a meta-analysis of 13 randomized controlled tion of pruritis. Residual hyperpigmentation trials.3 Additionally, the popular press and may take months to fade. general public’s rising interest are likely to in- crease the number of patients on this diet. Pharmaceutical intervention may be necessary A clinical diagnosis If additional treatment is required, minocy- The diagnosis is made clinically, so the appear- cline 100 to 200 mg/d has been reported most ance of a symmetric pruritic, hyperpigmented effective, likely due to its anti-inflammatory rash on the chest and back should prompt the properties.1,4 Topical corticosteroids and oral physician to ask about any recent changes in antihistamines provide symptomatic relief in diet. Laboratory analysis is unnecessary, as a some patients.1,4 complete blood count, basic metabolic panel, ❚ Our patient had resolution of the pru- and liver function panel are almost always nor- ritis and urticarial lesions within 2 days of mal. Urinary ketones are present in only 30% to resuming a normal diet; however, residual 50% of patients; there is, however, an absence asymptomatic hyperpigmentation persisted. of blood ketones.1,4 A retrial of the ketogenic diet initiated a flare of the rash in the same distribution. It rapidly resolved with carbohydrate intake. JFP Other conditions can mimic CORRESPONDENCE prurigo pigmentosa Daniel Croom, MD, 34520 Bob Wilson Dr, Naval Medical Center Urticaria presents as individual lesions that San Diego, San Diego, CA 92134; [email protected] CONTINUED

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References 1. Kim JK, Chung WK, Chang SE, et al. Prurigo pigmentosa: clinico- 4. Oh YJ, Lee MH. Prurigo pigmentosa: a clinicopathologic pathological study and analysis of 50 cases in Korea. J Dermatol. study of 16 cases. J Eur Acad Dermatol Venereol. 2012;26: 2012;39:891-897. 1149-1153. 2. Abbasi J. Interest in the ketogenic diet grows for weight loss and type 5. James WD, Berger T, Elston D. Diseases of the skin appendages. 2 diabetes. JAMA. 2018;319:215-217. Andrews’ Diseases of the Skin: Clinical Dermatology. 12th ed. 3. Bueno NB, de Melo IS, de Oliveira SL, et al. Very-low-carbohydrate Philadelphia, PA: Saunders Elsevier; 2015:747-788. ketogenic diet v. low-fat diet for long-term weight loss: a meta- 6. Shevchenko A, Valdes-Rodriguez R, Hsu S, et al. Prurigo pigmen- analysis of randomised controlled trials. Br J Nutr. 2013;110: tosa: case series and differentiation from confluent and reticu- 1178-1187. lated papillomatosis. JAAD Case Rep. 2018;4:77-80.

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