Primary cutaneous mucinoses in connective tissue diseases as a diagnostic and prognostic challenge

Mucin deposition in the skin, a hallmark feature in dermatopathology, is frequently associated with connective tissue diseases such as lupus erythematosus, dermatomyositis, and, to a lesser extent, scleroderma. Although mucin deposition commonly accompanies specific skin lesions in lupus erythematosus, dermatomyositis, and sometimes scleroderma, its occurrence as a distinct clinical manifestation with defining histopathologic features is rare. Such presentations that are classified as primary cutaneous mucinoses not only aid in diagnosis but may also have prognostic implications. This study systematically reviews the literature to evaluate case demographics, clinical characteristics, histologic findings, immunologic markers, and treatment responses of primary cutaneous mucinoses linked to connective tissue diseases. Our findings highlight that mucin deposition exhibits variable presentations and serves as a valuable diagnostic clue, particularly when integrated with other clinical and histopathologic criteria. Mucin, a high-molecular-weight glycoprotein complex primarily composed of hyaluronic acid, is a standard component of dermal connective tissues. It is produced in small amounts by fibroblasts and mast cells and is known for its high water-holding capacity. Excessive mucin deposition, however, which can occur in certain pathologic states, leads to dermal swelling known as myxedema. Cutaneous mucinosis is often associated with connective tissue diseases, in which mucin deposition can serve as histologic evidence for conditions such as lupus erythematosus (LE) or dermatomyositis (DM), particularly in the appropriate clinical context. Less frequently, mucin is also observed in scleroderma cases.^1,2 Although mucin deposition can accompany specific skin lesions in LE and DM, cases in which it is a prominent and defining histopathologic feature are rare. Such cases classified into the chapter of primary cutaneous mucinoses have diagnostic value and may also serve as prognostic indicators. This review assesses the diagnostic and prognostic significance of primary cutaneous mucinoses associated with connective tissue diseases.