Discussion
We experienced a case of subungual abscess with paronychia that improved with manual drainage without antibiotics. Among the numerous reviews on subungual tumors using US and MRI,1–4 the most comprehensive is that of Mundada et al..1 This review broadly divided subungual tumors into nail tumors and nail tumor-like lesions (e.g., mucoid cyst and epidermoid cyst). Nail tumors are divided into benign (e.g., glomus tumors and subungual exostosis, etc.) and malignant tumors (e.g., squamous cell carcinoma and malignant melanoma). They also stated that high-resolution MRI can identify subungual tumors better than X-ray or US although not in a perfect manner. However, four studies, including this one, did not include subungual abscesses. Subungual abscesses are mainly reported in case reports,5–7 and no reports included US or MRI images as far as we have examined. All these three cases were improved through CO2 laser drainage of the abscess and antibiotic treatment; however, the current case was improved through manual drainage without antibiotics. No studies have reported the organisms responsible for subungual abscesses; however, a study reported the organisms responsible for paronychia, with the Enterobacteriaceae family being the most common, followed by the Staphylococci genus .8 The causative organism in our case wasS. aureus , which is the most common member of theStaphylococci genus . Paronychia has been reported to be more common in occupations that involve frequent handling of water, such as bartenders, housekeepers, housemakers, dishwashers, and swimmers.8 The patient in the present case was a healthcare worker who frequently washed his hands because of the COVID-19 pandemic, which may have caused the subungual abscess. Anticancer agents, such as taxanes and anthracyclines, have also been reported as a cause of subungual abscesses, but no drugs were used in the present case.9
Ávila de Almeida et al. reported one subungual tumor, a glomus tumor, using a 33 MHz transducer with very sophisticated US images while previous US studies of subungual tumors were reported using a 15–18 MHz transducer.10 We clearly delineated a subungual abscess before and after treatment using a high-frequency transducer of 2–22 MHz in the present case, similar to that reported by Ávila de Almeida et al.
Abscesses should also be listed in the differential diagnosis of subungual tumors, and this is the first report of a subungual abscess that included US and MRI images.