Correspondence Address:
Eun Joo Park
Department of Dermatology, College of Medicine, Hallym University Sacred Heart Hospital, Anyang, Gyeonggi-do
South Korea

Full Text



Sir,

Digital mucous cysts (DMCs) are common pseudotumours occurring on the dorsum of the distal phalanges of fingers. They are also called dorsal finger cysts, myxoid cysts and focal myxomatous degeneration, reflecting the lesions' controversial nature. Organising thrombus, which contains fibrous tissue structured into layers, has rarely been reported as a skin nodule. We report a case of DMC proximal to an organising thrombus.

A 46-year-old man visited our clinic with complaints of an asymptomatic nodule on the left third finger for one year. The nodule was not ruptured or treated before. On examination, a solitary pea-sized firm nodule was observed on the proximal nail fold area on the left third finger [Figure 1]a. Punch biopsy showed a well-demarcated onion-shaped nodule containing fibrous tissue that was structured into layers with central calcification, consistent with an organising thrombus [Figure 2]a. Because symptoms were absent, no additional treatment was administered. After 2 months, the patient revisited our clinic with a new translucent solitary cystic nodule at a site proximal to the pre-existing lesion [Figure 1]b. For further management, we recommended orthopaedic surgery, and excisional biopsy was performed, which showed a mucinous lesion with surrounding fibrous stroma and pseudoepithelial lining, consistent with a myxomatous type of DMC [Figure 2]b. Subsequently, the patient was on follow-up and no additional new lesions manifested.{Figure 1}{Figure 2}

A thrombus is a clotted mass of blood that can occur anywhere in the cardiovascular system. While thrombi may resolve, some can undergo organisation due to the ingrowth of smooth muscle cells, fibroblasts and endothelium into the fibrin-rich thrombus.[1] If recanalisation fails to occur, the thrombus can develop into a fibrous scar that permanently obstructs blood flow.[1] Digital vein thrombosis can occur in the hands and feet, and there are many case reports of it as palmar lesions. However, it has not been reported in periungal lesions, especially as an organising thrombus.

DMCs can be classified into two types: Ganglion type is caused by the herniation of synovial linings or tendon sheaths, associated with degenerative joint disease and osteophytes and myxomatous type is thought to arise from the metaplasia of dermal fibroblasts, leading to excess hyaluronic acid production.[2],[3]

Our patient's DMC pathophysiology may be related to the prior punch biopsy of organising thrombus. Mechanical and inflammatory insults imposed by the biopsy might have provided specific weak points at the synovial lining, allowing the synovial fluid to leak and irritate surrounding tissue; the tissue reacted by forming a pseudocapsule and a subsequent ganglion.[4] The DMC in our case might also be related to the metabolic derangement of fibroblasts. According to Angelides,[5] recurrent stress and microtrauma at the synovial capsular interface may stimulate mucin production by fibroblasts. Therefore, mechanical and inflammatory insults imposed by the biopsy might have also stimulated fibroblast metaplasia, leading to mucin production and DMC formation.

To our knowledge, DMC occurring after an organising thrombus has not been previously reported. In this case, because the DMC occurred next to the organising thrombus after a punch biopsy, we speculate that mechanical and inflammatory insults imposed by the biopsy might have affected the formation of DMC.

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Conflicts of interest

There are no conflicts of interest.

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