Cutaneous focal mucinosis

Cutaneous focal mucinosis was first described by Johnson and Helwig in 1966 as a "degenerative" skin lesion characterized by increased mucin deposition in the dermis.

Cutaneous focal mucinosis is a "pseudotumorous" skin disease characterized by the presence of localized, non-encapsulated deposits of proteoglycans (mucins) in the dermis. It can appear solitary (solitary cutaneous focal mucinosis) or multiple (multiple cutaneous focal mucinosis) and is then frequently associated with systemic diseases (Kuo KL et al. 2017).

In 2016, it was proposed to use the terms

• solitary cutaneous focal mucinosis

and

• multiple cutaneous focal mucinosis

were introduced to differentiate solitary cutaneous focal mucinosis from multiple cutaneous focal mucinosis, as the latter is often associated with systemic diseases (Kuo KL et al. 2017).

The etiology of cutaneous focal mucinosis is unknown.

Pathogenetically, solitary cutaneous focal mucinosis can be described as a circumscribed skin lesion defined by the presence of mucin, a hyaluronic acid complex, in the dermis. The lesion typically appears as a solitary, asymptomatic papule on the extremities or back. It is not associated with systemic disease.

Multiple cutaneous focal mucinosis can be limited to the integument, but can also be associated with systemic diseases. Associated systemic diseases include Birt-Hogg-Dubé syndrome, systemic scleroderma, scleromyxoedema, systemic lupus erythematosus and thyroid diseases (Truhan AP et al.1986; Rongioletti F et al. 2001;Chen HH et al. 2004; Cohen PR et al. 2020).

Clinically, cutaneous focal mucinosis typically presents as asymptomatic flesh-colored, but also reddish, soft to soft-elastic, flat papules.

The predominant pathologic feature of cutaneous focal mucinosis is unencapsulated mucin, a hyaluronic acid complex, in the upper dermis. It can be visualized as mild basophilic staining on sections stained with hematoxylin and eosin. Although the diagnosis can be made on sections stained with hematoxylin and eosin, stains that detect mucin (such as alcian blue, colloidal iron, and toluidine blue) can be helpful in confirming the diagnosis.

1. Biondo G et al (2019) Clinical, dermoscopic, and histologic aspects of two cases of cutaneous focal mucinosis. An Bras Dermatol 94:334-336.

2. Chen HH et al (2004) A solitary soft fibroma-like polypoid mucinosis: report of an unusual case. Dermatol Surg 30:450-451.
3. Cohen PR et al (2020) Case report and review of solitary cutaneous focal mucinosis: a unique primary cutaneous mucinosis unrelated to mucinosis-associated systemic diseases. Dermatol Online J 26:13030/qt33m815p3.
4. Erickson CP et al (2020) Case report and review of solitary cutaneous focal mucinosis: a unique primary cutaneous mucinosis unrelated to mucinosis-associated systemic diseases. Dermatol Online J 26
5. Gutierrez N et al (2021) Solitary cutaneous focal mucinosis. Cureus 13:e18618.
6. Jakubovic HR et al (1982) Multiple cutaneous focal mucinoses with hypothyroidism. Ann Intern Med 96:56-58.
7. Johnson WC et al (1966) Cutaneous focal mucinosis. A clinicopathological and histochemical study. Johnson WC, Helwig EB. Arch Dermatol 93:13-20.
8. Kuo KL et al (2017) Solitary cutaneous focal mucinosis: a clinicopathological study of 11 cases of soft fibroma-like cutaneous mucinous lesions. J Dermatol 44:335-338.
9. Lindor NM et al (2001) Birt-Hogg-Dube syndrome: an autosomal dominant disorder with predisposition to cancers of the kidney, fibrofolliculomas, and focal cutaneous mucinosis. Int J Dermatol 40:653-656.
10. Rongioletti F et al (2001) Cutaneous mucinoses: microscopic criteria for diagnosis. Am J Dermatopathol. 23:257-267.
11. Truhan AP et al (1986) The cutaneous mucinoses. Truhan AP, Roenigk Jr HH. J Am Acad Dermatol14:1-8.
12. Schneider BV et al (1991) Nodular cutaneous mucinosis--an unusual multiple type of euthyroid focal mucinosis. Dermatologica 183:73-76.
13. Verma G et al (2018) Trauma-induced focal nodular mucinoses: a rare entity. Indian Dermatol Online J 9:50-52.