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.