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Clinical Updates

Yoshiki Miyachi, MD, PhD

Skin Diseases First Described by Japanese Dermatologists. Part 2: Prurigo Pigmentosa

Yoshiki Miyachi

Wednesday, May 11, 2011

Prurigo pigmentosa (PP) is an inflammatory skin disease characterized by intensely pruritic papules distributed on the back, neck and chest, leaving gross reticular or net-like pigmentation that occurs mainly in young women (Figure 1). Exacerbations and recurrences are the rule. Although more than 200 patients with this condition have been reported, mainly from Japan, over 40 cases in the literature are from other Asian and Western countries. Whether PP really has a proclivity for the Japanese or whether it is just underdiagnosed outside Japan still remains unclear; however, once you have encountered a patient with PP, you will remember the case because of its impressive clinical manifestations, as well as its prompt clinical response to minocycline or dapsone.


Figure 1. Early lesions (left-hand images) and late lesions (right-hand images) on the back of two patients with prurigo pigmentosa.

In this article, we will review the clinical presentation, histopathology and treatment of patients with PP.

What is PP?

PP was first reported by Professor Nagashima (1929-2010) of Kyorin University in 1971 in the Japanese Journal of Dermatology as "a peculiar pruriginous dermatosis with gross reticular pigmentation".1 His English publication in the Journal of Dermatology followed in 1978 and coined the novel name of "prurigo pigmentosa".2

As illustrated in Figure 2, the sudden onset of erythematous papules with severe pruritus is noticed initially, developing into reticular pigmentation that is symmetrically localized on the trunk. Clinically, diagnoses of dermatitis herpetiformis, poikiloderma atrophicans vasculare, confluent and reticulated papillomatosis, reticulate pigmented dermatosis and pigmented contact dermatitis are excluded by their different symptoms and clinical courses, as well as different histopathology. As such, PP is now recognized as a distinct inflammatory disease of the skin.3,4


Figure 2. Typical clinical course of prurigo pigmentosa. Early pruriginous pruritic papules (top image) and fully developed skin legions leaving gross reticular pigmentation (bottom image).

The etiology and pathogenesis of PP still remain unclear; however, reported causative factors include ethnic predisposition, environmental causes, seasonal variation, mechanical stimuli (eg, friction from cloths), contact allergens (eg, chrome and nickel), and ketosis as a consequence of diabetes mellitus, anorexia nervosa or dieting.5

Histopathology of PP

By studying 25 patients with PP and reviewing 178 cases in the literature, Boer and Ackerman6 reported that histopathological changes transpire rapidly, as do the clinical features throughout the entire disease course. Although most papers in the literature have described the histopathology as merely non-specific lichenoid dermatitis, PP involves dynamic changes from superficial perivascular dermatitis, spongiotic dermatitis, and lichenoid dermatitis to post-inflammatory hyperpigmentation, depending on the stage of the skin lesions.4 Importantly, neutrophils are found in early lesions of PP, as shown in Figure 3, which may explain why dapsone and minocycline are effective in the early stages, but ineffective in the late post-inflammatory pigmentation stage, of PP.6


Figure 3. Neutrophils are scattered in the papillary dermis in early skin lesions of prurigo pigmentosa.

Treatment of PP

Oral/topical corticosteroids and oral antihistamines are usually ineffective against PP. As most patients have usually been diagnosed with contact dermatitis or acute prurigo, and have received topical corticosteroids as well as antihistamines, they usually complain of a poor response to treatment.

Upon oral administration of minocycline or dapsone, pruritus will begin to be reduced within 24 h, and the clinical symptoms of PP will resolve completely if these drugs are given in the early stages of the disease. This success is so impressive that both patients and dermatologists will never forget such a case, even if experienced only once.

Regarding the mechanism of action of these drugs, it is thought that anti-inflammatory actions, through inhibition of the migration and/or function of neutrophils, may be responsible, because both minocycline and dapsone have been reported to modify neutrophilic functions, such as the generation of neutrophil-derived reactive oxygen species.7,8 Doxycycline and other sulfonamides are also effective, presumably because of their similar mechanism of action.9


Although PP is a rare inflammatory skin disease, it is not uncommon, even in non-Asian populations.10,11 It has highly characteristic clinical manifestations and responds well to appropriate treatment if a correct diagnosis is made. Increased recognition of this entity by the Western dermatologic community will greatly help in improving outcomes of patients with this condition.


  1. Nagashima M, Ohshio A, Shimizu N. A peculiar pruriginous dermatosis with gross reticular pigmentation [Japanese]. Jpn J Dermatol 1971;81:38-39.
  2. Nagashima M. Prurigo pigmentosa - clinical observations of our 14 cases. J Dermatol 1978;5:61-67.
  3. Joyce AP, Horn T, Anhalt GJ. Prurigo pigmentosa. Arch Dermatol 1989;125:1551-1554.
  4. Boer A, Misago N, Wolter M, et al. Prurigo pigmentosa: A distinctive inflammatory disease of the skin. Am J Dermatol 2003;25:117-129.
  5. Lu PH, Hui RC, Yang LC, et al. Prurigo pigmentosa: a clinicopathological study and analysis of associated factors. Int J Dermatol 2011;50:36-43.
  6. Boer A, Ackerman AB. Prurigo pigmentosa is distinctive histopathologiaclly. Int J Dermatol 2003;42:417-418.
  7. Miyachi Y, Niwa Y. Effects of potassium iodide, colchicine and dapsone on the generation of polymorphonuclear leukocyte-derived oxygen intermediates. Br J Dermatol 1982;107:209-214.
  8. Miyachi Y, Yoshioka A, Imamura S, et al. Effect of antibiotics on the generation of reactive oxygen species. J Invest Dermatol 1986;86:449-453.
  9. Miyachi Y, Yoshioka A, Horio T, et al. Prurigo pigmentosa: A possible mechanism of action of sulfonamides. Dermatologica 1986;172:82-88.
  10. Baykal C, Buyukbabani N, Akinturk S, et al. Prurigo pigmentosa: not an uncommon disease in the Turkish population. Int J Dermatol 2006;45:1164-1168.
  11. Boer A, Asgari. Prurigo pigmentosa: An underdiagnosed disease? Ind J Dermatol Venereol Leprol 2006;72:405-409.