Dear Editor,

Cutaneous mucinoses are a group of diseases in which there is an abnormal deposit of mucin in the skin. It can be classified into primary and secondary forms. An uncommon subtype of primary mucinosis, acral persistent papular mucinosis (APPM) is currently considered as a clinicopathological variant of lichen myxedematosus.

A 31-year-old woman presented a 10-year history of persistent pruritic lesions on her arms. She had no relevant medical history. Physical examination revealed multiple, non-follicular and small (2-5 mm) skin-colored papules, some of them translucent, on the dorsum of both forearms ([Figure 1](#f1){ref-type="fig"}). There were no other similar lesions on the rest of the body. The patient reported that topical corticosteroids were ineffective and sun exposure increased the number of lesions. Laboratory studies were within normal range, including blood cell count, liver, kidney and thyroid function. Antinuclear antibodies were negative. Skin punch biopsy of a papule was performed and histopathological examination showed no alteration in the epidermis. There was a focal area in the upper and mid reticular dermis due to a separation of collagen fibers. Deposit of mucin in the papillary dermis that stained positively with alcian blue was observed. There was no deposit of mucin in the reticular dermis. Fibroblast proliferation was not evident ([Figure 2](#f2){ref-type="fig"}). APPM was then diagnosed.

Figure 1Small skin-colored papules, some of them translucent, symmetrically located on the dorsum of both forearms

Figure 2Epidermis shows no alterations. Note the focal area in the upper and mid reticular dermis due to a separation of collagen fibers. The area is positively stained with alcian blue, indicating deposit of mucin (Alcian blue, x40)

APPM was first described by Rongioletti *et al.* in 1986^[@r1]^ and the etiology is unknown, although both genetic and environmental factors are thought to play a role. Rongioletti and Rebora in 2001 proposed several diagnostic criteria for APPM and, to date, there have been more than 30 reported cases of this entity that met the criteria ([Table 1](#t1){ref-type="table"}).^[@r2]^ Three cases showed family history.^[@r3]^ Clinically, it is characterized by small flesh-colored, papules that most often are symmetrically localized on the back of the hands, wrists and extensor aspects of distal forearms. Differential diagnosis includes lichen nitidus, common warts and other forms of mucinosis. The lesions are usually asymptomatic, although in our case they were very pruritic. They tend to persist and may increase slowly. There is a female predominance. Neither systemic disease nor monoclonal gammopathy in peripheral blood are observed in this entity. The possible association with malignancies has not been clarified yet.^[@r4]^ The typical histopathology of APPM is a focal, well-circumscribed deposit of mucin in the papillary and mid-dermis. The deposit never extends to the deep reticular dermis. Fibroblastic proliferation is variable, although normally they are not increased in number. Due to the absence of symptoms, treatment is rarely necessary. APPM has been treated with topical corticosteroids, tacrolimus, pimecrolimus, liquid nitrogen, electrocoagulation and Erbium-YAG laser with some success.^[@r5]^ In our case, the patient reported pruritus, so we treated with topical 0.1% tacrolimus ointment for five weeks, but it was ineffective. We prescribed a fluid emulsion 12% sodium lactate for two months and the symptoms disappeared. We herein present a new case of this rare mucinosis. It is important to know that most cases are asymptomatic, but in our case, the patient presented pruritic lesions.

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Diagnostic criteria for APPM

  Clinical Criteria                                  Histopathological Criteria
  -------------------------------------------------- ---------------------------------------------------------------------------
  Multiple, small (2-5 mm) papules                   Focal, well-circum­scribed amount of mu­cin in the upper reticular dermis
  Located exclusively on hands, wrists or forearms   No deposit of mucin in the deep reticular dermis
  Persistent and may increase in number              Mucin spares a subepi­dermal zone
  Predominates in women                              Fibroblast proliferation is usually absent
  No evidence of systemic disease                     
  No associated with gammopathy                       

Modified from: Pérez-Mies, *et al*, 2006.^[@r2]^

Work conducted at the Hospital Universitari Sagrat Cor, Barcelona, Spain.

Conflict of interest: None.

**AUTHORS\'CONTRIBUTIONS**

Ana Iglesias-Plaza

0000-0001-6628-274X

Approval of the final version of the manuscript, Design and planning of the study, Preparation and writing of the manuscript, Collecting, analysis and interpretation of data, Effective participation in research orientation, Intellectual participation in propaedeutic and/or therapeutic conduct of studied cases, Critical review of the literature, Critical review of the manuscript

Gemma Melé-Ninot

0000-0003-0365-0634

Approval of the final version of the manuscript, Design and planning of the study, Preparation and writing of the manuscript, Collecting, analysis and interpretation of data, Effective participation in research orientation, Intellectual participation in propaedeutic and/or therapeutic conduct of studied cases, Critical review of the literature, Critical review of the manuscript

Noelia Pérez-Muñoz

0000-0002-5144-1784

Approval of the final version of the manuscript, Collecting, analysis and interpretation of data , Effective participation in research orientation, Critical review of the literature

Montse Salleras-Redonnet

0000-0003-1004-2493

Approval of the final version of the manuscript, Critical review of the literature
