Prurigo pigmentosa (PP) is a rare acquired inflammatory dermatosis with peculiar clinical and histological features. The disease, which predominantly occurs in young women, has been most frequently reported in Japan. In a review of the literature, we found only a few cases of PP in non-Japanese patients compared with more than 300 in Japanese patients.1 Although ethnicity and environmental factors have been claimed to play a role in the pathogenesis of PP, so far no cause has been identified for this striking eruption. We describe monozygotic white twins who both developed PP.
Twin 1 was referred in her late 20s for evaluation of a 10-year history of chronic relapsing highly pruritic dermatosis affecting predominantly the upper chest and back. She was previously treated with topical corticosteroids without improvement. She had a medical history of atopic dermatitis. Her family history was unremarkable except for her twin sister (twin 2), who had a 4-year history of a similar eruption.
Physical examination of twin 1 revealed symmetrically distributed erythematous papules and papulovesicles and confluent pigmented macules with a netlike reticular pattern on her chest in the intermammary cleft (Figure 1A) and on the upper and lower back (Figure 1C). Light microscopy studies of a skin biopsy specimen obtained from the upper back showed an epidermis with spongiosis, focal lichenoid changes with few necrotic keratinocytes, and a superficial perivascular infiltrate of lymphocytes, eosinophils, and few neutrophils (Figure 2). The patient was given doxycycline, 50 mg/d, which resulted in a rapid improvement of the acute lesions, whereas the postinflammatory reticular pigmentation persisted.
Twins 1 and 2 had virtually identical inflammatory lesions, which resulted in postinflammatory hyperpigmentations in a vaguely reticular pattern.
Epidermis shows spongiosis, focal lichenoid changes, few apoptotic keratinocytes, superficial mixed inflammation with some neutrophils and pigment incontinence (hematoxylin-eosin, original magnification ×40).
Twin 2 (Figure 1, B and D) presented some months later for evaluation of a 4-year history of relapsing eruption associated with severe itching. On examination, she had macular reticular pigmentation symmetrically distributed on her lower and upper back and chest. The most recent eruption, which started while the patient was abroad for some months, predominantly relapsed in spring and autumn. In the absence of acute lesions and based on the clinical presentation identical to that of her twin sister, no skin biopsy was performed.
Monozygotic twins each presented with a similar pruritic relapsing eruption, the clinicopathological features and evolution of which were characteristic for PP. As observed in these cases, PP is characterized by itching erythematous and urticarial papules and papulovesicles arranged in a reticular pattern and distributed symmetrically on chest, back, posterior neck, and shoulders. The lesions usually resolve in few days or weeks. Recurrences are frequent and finally result in postinflammatory reticulated netlike hyperpigmentations. Light microscopy findings depend on the stage of the disease, showing early, fully developed, and late changes. They variably encompass superficial perivascular neutrophilic infiltrate, lichenoid changes, necrotic keratinocytes, and vacuolar alterations. In late stages, there is often a hyperpigmented epidermis with dermal melanophages.2 As previously reported, minocycline and doxycycline are often effective in PP,3 as in our patients.
The cause of PP is unknown. Several triggering factors have been discussed, including sunlight, nutritional factors including dieting, diabetes, and ketonuria.4 There was no evidence for such putative triggers in these 2 patients. The development of PP 6 years apart in 2 monozygotic white twins is striking, especially since there was no family history, and to our knowledge, it is unique. Our observation in monozygotic twins thus raises the question of the importance of genetic factors for the development of PP. The idea that genetic predisposition is involved in PP is further supported by recent reports describing 3 cases of PP with segmental distribution suggesting a genetic cutaneous mosaicism.5,6 The presence of neutrophils in the inflammation and the improvements with Dapsone suggests a key pathophysiological role of neutrophils in this disease.
Corresponding Author: Carine Houriet, MD, Department of Dermatology, Inselspital, Bern University Hospital, University of Bern, Freiburgstrasse, Bern 3010, Switzerland (email@example.com).
Published Online: January 11, 2017. doi:10.1001/jamadermatol.2016.4921
Conflict of Interest Disclosures: None reported.
Houriet C, Perruchoud DL, Beltraminelli H, Borradori L. Prurigo Pigmentosa in White Monozygotic Twins. JAMA Dermatol. Published online January 11, 2017. doi:10.1001/jamadermatol.2016.4921