Lichen myxedematosus (LM) is a chronic cutaneous mucinosis that can present as a localized skin lesion or as a generalized systemic disease termed scleromyxedema. The differential diagnosis is determined by a combination of clinical presentation, serological studies, and histopathological examination. Currently, well-established and accepted histopathological features to distinguish localized LM from scleromyxedema have not been elucidated. Our recent publication, together with a retrospective literature review, suggests that the presence of groups of light chain-restricted plasma cells represents a distinct histopathological clue for the diagnosis of localized LM. In this report, we provide two additional cases of localized LM with lambda light chain-restricted plasma cells, together with clinical and histopathological findings that are similar to our previous publication. These cases support our theory that the light chain-restricted plasmacytic microenvironment is primarily attributed to the pathogenesis of localized LM. Therefore, we consider these cases to constitute a clinically and pathologically new variant of localized LM and name it primary localized cutaneous LM with light chain-restricted plasma cells.

BACKGROUND: Acral persistent papular mucinosis (APPM) is a rare idiopathic subtype of localized lichen myxedematosus. To date, there have been 40 APPM cases reported worldwide; however, only 7 cases have been reported in the Korean literature.
METHODS: A 70-year-old man was referred to our hospital with a solitary pinkish nodule on the dorsum of his right hand. Despite the absence of symptoms, the patient wanted to know the exact diagnosis; thus, a biopsy was performed. Histopathological examination of a biopsy specimen obtained from the nodule on the dorsum of his hand revealed orthokeratotic hyperkeratosis with patchy parakeratosis, prominent hypergranulosis, and diffuse dissecting mucinous deposition between collagen bundles, along with some bland-looking spindle cells throughout the dermis. The nodule was histologically diagnosed as an APPM, and an intralesional triamcinolone injection (2.5 mg/mL) was started every 2 wk. After three sessions of treatment, the patient showed marked improvements.
CONCLUSIONS: To the best of our knowledge, this is the first case of a Korean APPM presenting as a solitary nodule that showed a marked response to triamcinolone intralesional injection. Since it is a rare disease, we report this case to contribute to future research on the pathogenesis and treatment of APPM.