Case Report
The patient was a 47-year-old Japanese male healthcare worker who had no specific medical history, allergies, oral medications, or family history. He has smoked 20 cigarettes a day for the past 10 years and is only an occasional drinker. He frequently washed his hands because of the coronavirus disease-2019 (COVID-19) pandemic. Approximately 4 months ago, he noticed an abnormality in his left first fingernail, which had a vertical white line. He believed the nail abnormality was caused as a result of losing 10 kg body weight in an attempt to get into shape. Approximately 2 weeks ago, he gradually developed swelling, heat, and tenderness around the left first fingernail; thus, he visited the rheumatology and orthopedics department of our hospital. He had no other symptoms, i.e., fever or arthralgia. His vital signs were as follows: blood pressure 135/72 mmHg, pulse 80 beats/minute, respiratory rate 12 breaths/minute, and SpO2 99% (room air). The physical examination revealed a swollen entire left first fingertip compared with the right first fingertip and a reddish proximal nail fold with evidence of paronychia. In addition, he had tenderness when pressing on the proximal nail fold and the proximal end of the nail plate (Figure 1). The X-ray revealed no fractures or bone erosion; however, soft tissue swelling was observed in the vicinity of the nail and at the palmar distal pulp (Figure 2). We performed MRI of the left fingers using a 3 Tesla scanner without contrast media (Ingenia 3.0T, Philips Healthcare, Best, the Netherlands). MRI showed a tumor with low intensity on T1-weighted axial image and high intensity on T2-weighted axial image and the short-tau inversion recovery (STIR) sagittal image between the nail plate and the distal phalanx (Figure 3). The tumor had a relatively long extension both vertically and horizontally. A rheumatologist with 8 years of experience performed a high-frequency US examination using the ARIETTA 850 device (FUJIFILM Healthcare Corporation, Tokyo, Japan) with a 2–22 MHz transducer. The US image revealed an oval and well-defined tumor between the nail plate and the distal phalanx. The tumor was pushing up the nail root. The interior of the tumor was plastic with abundant blood flow within the tumor (Figure 4, Supplementary Videos 1). The patient then pressed the proximal nail fold and found pus from the onychodermal band (Figure 5). Culture examination revealed a beta-lactamase-producing form ofStaphylococcus aureus (S. aureus ), which was resistant to penicillin G and aminobenzylpenicillin but suitably sensitive to other antibiotics. Manual pressing of the proximal and bilateral nail folds resulted in adequate drainage and immediate improvement of symptoms without antibiotics, and the nail was completely improved in 4 months (Figure 6). At the same time, the nail improved, and MRI and US showed a complete resolution of the subungual abscess (Figure 7, Supplementary Videos 2). Therefore, a final diagnosis for the subungual abscess was established. No recurrence has been observed since then.