The superficial dermatomycoses tinea nigra (TN), white piedra (WP), and black piedra (BP) are most often caused by Hortaea werneckii, Trichosporon spp., and Piedraia hortae, respectively, and typically diagnosed in tropical regions.¹ Globally, the largest studies include only 50 TN, 131 WP, and 74 BP cases.^2–4 Updated epidemiologic and clinical data might help prevent misdiagnosis (eg, TN vs melanoma) and support timely treatment.¹ Therefore, we analyzed TN, WP, and BP in a large health insurance database.

Using the 2019–2023 Merative MarketScan Commercial databases, we identified outpatients with TN, WP, or BP diagnosis codes (Supplementary Material, available via Mendeley at https://data.mendeley.com/datasets/k7tyvj82sy/1). We estimated 5-year prevalence, stratifying by demographic characteristics, and described previous diagnoses and underlying medical conditions, laboratory testing, outpatient antifungal prescriptions, and specialty types seen.

Among 39,388,096 outpatients, 879 had TN (prevalence [ per 1 million]:22.3), 317 WP (8.0), and 47 BP (1.2) (Table I). BP was not further analyzed given small numbers. TN prevalence was highest for patients ≥65 years (28.1) and lowest for <18 years (19.4); WP prevalence was similar for patients ≥65 years (10.3) and <18 years (11.2) and lowest for 18–44 years (6.5). For both conditions, prevalence was similar for male vs female patients (TN:21.5 vs 23.0, WP:8.5 vs 7.6), highest in the South (TN:26.1, WP:9.2) or Northeast (TN:23.8, WP:10.8), and lowest in the West (TN:15.1, WP:5.3).

For TN and WP patients, a similar percentage had diabetes mellitus (TN:9%, WP:9%), hyperhidrosis (TN:1%, WP:<1% [n = 1]), and immunocompromising conditions (TN:5%, WP:6%) (Table II). Among TN patients, 3 (<1%) were previously diagnosed with melanoma. Laboratory testing was documented in 14% of TN and 6% of WP patients, most frequently biopsy/histopathology (TN:9%, WP:5%). Most patients received antifungals (TN:56%, WP:56%), primarily topical (TN:47%, WP:44%), most frequently ketoconazole (TN:23%, WP:23%). Nine percent of TN and 11% of WP patients received an oral antifungal, most frequently fluconazole (TN:5%, WP:7%). The most common specialty types seen for TN were dermatology (40%) and general practice (24%) and for WP were general practice (34%) or pediatrics (19%).

To our knowledge, this is the largest published study of TN and piedra. These conditions were rare (each diagnosed in <25 per million US outpatients during 2019–2023) and affected generally healthy persons, consistent with limited previous literature.^1,5 Awareness of TN epidemiology is particularly important given the potential to avoid biopsies (received by 9% of TN patients) for suspected melanoma and to ensure proper treatment. Previous reports emphasize TN and WP in tropical climates, particularly among female children and hyperhidrosis patients.^1,5 We found similar TN and WP prevalence across sexes and higher (TN) or similar prevalence (WP) in older adults vs children. Cases occurred across US regions (with Southern prevalence similar to Northeastern), potentially reflecting travel or migration, and hyperhidrosis was infrequently documented.

Our study lacked information on non-commercially–insured patients, over-the-counter treatments, treatment response, utilization of special stains, and dermoscopy, a useful diagnostic tool for TN.²

Our analysis highlights the presence of TN, WP, and BP in the United States, emphasizing the importance of physician awareness to ensure prompt recognition and treatment.