BACKGROUND: Various skin findings due to coronavirus have been identified. There are a few case reports on nail findings after coronavirus (COVID-19) infection. We aimed to document the nail findings of the COVID-19 survivors and shed light on the interesting luminescence seen under the Wood\'s light.
METHODS: One hundred and seventy-four patients diagnosed with COVID-19 infection in the last 100 days were grouped in terms of the agents used in the treatment. Fifty-seven volunteers without a history of infection were included.
RESULTS: Patients treated with favipiravir had a significantly higher positivity of luminescence (p: 0.0001). The most common nail findings in patients were splinter hemorrhage (13%), followed by leukonychia (12%) and longitudinal ridges (7.9%).
CONCLUSIONS: The luminescence may be seen due to the accumulation of favipiravir or its excipients (titanium dioxide and yellow ferric oxide) on the nails. Wood\'s lamp examination of the plasma taken from a patient after favipiravir\'s first dose revealed the same luminescence as we saw on the nails. Accordingly, this accumulation may be seen in the vital organs. Although our knowledge about the virus increases day by day, the potentially hazardous effects of the virus and long-term complications of the treatment options are still being investigated.

Nail examination must be an essential part of physical examination in our daily clinical practice, as nail changes may be the revealing sign of systemic diseases in the absence of other alarming signs.

This is a case of systemic polyarteritis nodosa (PAN) in a 43-year-old male who initially presented to the hospital with a puzzling collection of signs and symptoms, including fever, arthralgias, myalgias, abdominal pain, dark urine, and rash. His illness evolved over the course of four weeks, and skin biopsy helped to clinch the diagnosis and lead to appropriate treatment. It is important to consider systemic PAN in the work-up of patients with subtle skin findings in the context of seemingly unrelated constitutional, abdominal, genitourinary, cardiac, and neurological signs and symptoms.

BACKGROUND: Patients with psoriatic arthritis (PsA) commonly present with nail manifestations; however, little is known about these manifestations.
OBJECTIVE: This study investigated whether nail findings can be used to discriminate between PsA and psoriasis without arthritis.
METHODS: We performed a retrospective analysis of 118 patients with PsA and 974 patients with psoriasis without arthritis who visited St. Luke\'s International Hospital (Tokyo, Japan) between July 2003 and February 2015. Patients with PsA were classified according to the Classification of Psoriatic Arthritis criteria. Skin lesion severity was assessed by using the Psoriasis Area and Severity Index, and 9 types of nail findings were investigated.
RESULTS: The incidence of nail involvement in patients with PsA was 67.6%. Female sex, presence of transverse grooves, onycholysis, and splinter hemorrhages were significantly related to PsA, with transverse grooves demonstrating the strongest association (odds ratio, 5.01; 95% confidence interval, 2.31-10.8; P < .01). Furthermore, the presence of transverse grooves was strongly related to both distal interphalangeal arthritis and enthesitis.
CONCLUSIONS: The PsA population was relatively small.
CONCLUSIONS: Nail findings enabled us to distinguish patients with PsA from those without arthritis. The presence of transverse grooves is significantly associated with PsA and may be associated with distal interphalangeal arthritis and enthesitis.