Dear Editor,

Prurigo pigmentosa (PP), also known as Nagashima's disease, is a rare inflammatory dermatosis characterized by pruritic erythematous papules or macules arranged in a reticular pattern. PP is often misdiagnosed and therefore many patients are incorrectly treated. A 25-year-old Caucasian patient was admitted to our clinic showing erythematous, itching papules on his chest, back, and neck, which have developed within three weeks (Figure 1A). His medical history was negative for allergy and other dermatoses and his family history was also negative for relevant dermatoses. Interestingly, the patient reported a recent dramatic change in his diet, starting a strict ketogenic diet for weight loss. A previous local therapy with medium-potency corticosteroids led only to a mild improvement. Histologically, a mild elongation of rete ridges associated with spongiosis and perivascular infiltration of lymphocytes and eosinophils was observed (Figure 1B). According to the clinical and histopathological features, a diagnosis of PP was established. The patient was treated with oral doxycycline 100 mg/day over 10 weeks, showing initially a partial resolution after four weeks and later a complete resolution of the clinical picture (Figure 1C). PP is a rare inflammatory dermatosis, which usually affects adolescents and young adults.¹ Although PP has been mainly described in Asiatic patients, several reports described PP in patients of Caucasian, Hispanic, and African descent.² Usually, patients show itchy, erythematous papules or macules on the back, chest, and neck, which are typically arranged in a reticulated pattern.² The pathogenesis of PP is still unknown, but in more than 50% of cases aggravating factors have been identified, including dietary changes, friction, sweat, ketonuria, and hormonal changes. Furthermore, in the group of patients who reported dietary changes, about 40% reported a strict adherence to a ketogenic diet before the onset of PP.² Pregnancy was also identified as an exacerbating factor.³ In addition, PP has been reported in patients with adult-onset Still disease. In this case, increased interleukin (IL) 6 expression in PP lesions was reported.⁴ Histologically, PP lesions can show several features. The most frequent epidermal changes include orthokeratosis, epidermal hyperplasia, spongiosis, and basal cell vacuolization, while frequent dermal changes are represented by perivascular polymorphonuclear and lymphocyte infiltrate, and papillary dermal edema.¹ Several clinical differential diagnoses should be considered, including contact dermatitis and confluent and reticulated papillomatosis (CARP). However, CARP shows usually hyperkeratotic papillomatous lesions, which are not detected in PP. Furthermore, CARP shows histologically neutrophilic exocytosis, interface dermatitis, spongiosis with vesiculation, and dyskeratosis.⁵ Tetracyclines are the first-choice therapy for PP.¹ Minocycline is usually administered as monotherapy, but sometimes it is used in combination with topical corticosteroids.¹ Doxycycline as monotherapy represents an alternative therapy. Regarding doxycycline, it has been reported, that the mean resolution period was ca. 23 days, and that a recurrence can occur in ca. 10% of patients after withdrawal of the therapy.¹ In addition, modifying patients' dietary habits can be useful in some cases.² In conclusion, dermatologists should review patients' dietary habits in case of a pruritic, reticulated rash on the trunkand consider PP as potential diagnosis.

亲爱的编辑，

色素性痒疹 (PP)，也称为长岛病，是一种罕见的炎症性皮肤病，其特征是瘙痒性红斑丘疹或斑点呈网状排列。PP 经常被误诊，因此许多患者得到不正确的治疗。一名 25 岁的白人患者因胸部、背部和颈部出现红斑、瘙痒丘疹而入院，该丘疹在三周内出现（图 1A）。他的病史没有过敏和其他皮肤病，他的家族史也没有相关皮肤病。有趣的是，该患者报告说他的饮食最近发生了巨大变化，开始严格的生酮饮食以减轻体重。先前使用中效皮质类固醇进行局部治疗仅导致轻微改善。组织学上，观察到与淋巴细胞和嗜酸性粒细胞的海绵化和血管周围浸润相关的网状脊的轻度伸长（图 1B）。根据临床和组织病理学特征，建立了 PP 的诊断。患者在 10 周内接受口服多西环素 100 mg/天治疗，最初显示 4 周后部分消退，后来临床表现完全消退（图 1C）。PP 是一种罕见的炎症性皮肤病，通常影响青少年和年轻人。最初显示 4 周后部分消退，后来临床表现完全消退（图 1C）。PP 是一种罕见的炎症性皮肤病，通常影响青少年和年轻人。最初显示 4 周后部分消退，后来临床表现完全消退（图 1C）。PP 是一种罕见的炎症性皮肤病，通常影响青少年和年轻人。¹虽然 PP 主要在亚洲患者中得到描述，但一些报告描述了高加索人、西班牙裔和非洲人后裔患者的 PP。²通常，患者会在背部、胸部和颈部出现发痒的红斑丘疹或斑疹，这些丘疹通常呈网状排列。² PP 的发病机制尚不清楚，但在超过 50% 的病例中已确定加重因素，包括饮食变化、摩擦、出汗、酮尿和激素变化。此外，在报告饮食变化的患者组中，约 40% 的患者报告在 PP 发作前严格遵守生酮饮食。²怀孕也被确定为一个恶化因素。^3个此外，PP 在成人 Still 病患者中也有报道。在这种情况下，报告了 PP 病变中白细胞介素 (IL) 6 表达增加。⁴在组织学上，PP 病变可以表现出多种特征。最常见的表皮变化包括正角化、表皮增生、海绵化和基底细胞空泡化，而频繁的真皮变化表现为血管周围多形核细胞和淋巴细胞浸润，以及乳头状真皮水肿。^1个应考虑几种临床鉴别诊断，包括接触性皮炎和融合网状乳头状瘤病 (CARP)。然而，CARP 通常显示角化过度的乳头状瘤样病变，而在 PP 中未检测到。此外，CARP 在组织学上表现出嗜中性粒细胞胞吐、界面性皮炎、海绵状水泡形成和角化不良。⁵四环素类药物是 PP 的首选疗法。¹米诺环素通常作为单一疗法给药，但有时与局部皮质类固醇联合使用。^1个多西环素作为单一疗法代表了一种替代疗法。关于多西环素，据报道，平均消退期为 ca。23 天，并且复发可能发生在 ca。10%的患者在停止治疗后。¹此外，在某些情况下，改变患者的饮食习惯可能会有用。²总之，如果躯干出现瘙痒性网状皮疹，皮肤科医生应检查患者的饮食习惯，并将 PP 视为潜在诊断。