Dermatophytic melanonychia: A case series of an increasing disease

Abstract

Background Melanonychia refers to brown‐black colour pigmentation due to melanin or not‐melanin deposition in the nail plate. Onychoscopy allows to distinguish if the pigmentation is due by melanin or not. The main causes of non‐melanic pigmentation are subungual haematoma and pigmented onychomycosis. Fungal melanonychia (FM) is rare and may present as diffuse or longitudinal pigmentation. Differential diagnosis includes melanic activation, such as ethnic‐type nail pigmentation or frictional melanonychia, but also versus melanic proliferation, such as nevus or nail melanoma. Fungal melanonychia can be due to a colonisation by fungi with black variant or by melanin activation due to inflammation of fungal invasion. Objectives The aim of paper is to increase clinical and dermoscopic knowledge of this increasingly frequent disease. Methods In this retrospective observational study, twenty patients with dermatophytic melanonychia were collected, with available clinical and dermoscopic pictures. The diagnosis of dermatophytic melanonychia was made based on clinical manifestation and mycological examination. KOH smear was performed in all cases. For each patient, clinical data included: age, gender, type of melanonychia and involved fingers. Results This study aimed to show increased incidence of dermatophytic melanonychia and its correct management. In addition, we reviewed our collected cases and described the clinical and dermoscopic features of dermatophytic melanonychia. Conclusions The results of this study showed that physicians should keep in mind the diagnosis of this increasing disease, and that it cannot be performed relying only on clinical grounds. We would like to highlight the importance of tools as KOH examination, culture and dermoscopy.

Diagnostic accuracy of dermoscopy for onychomycosis: A systematic review

“…Five studies reported dermoscopic features of 148 cases of fungal melanonychia ( Table 3 ) ( 29 – 31 , 33 ). These cases demonstrated longitudinal white or yellow streaks (52, 35.1%) ( 31 – 33 ), nail surface scales (39, 33.1%) ( 31 – 33 ) and subungual hyperkeratosis (41, 27.7%) ( 31 – 33 ) ( Table 3 ), which are also common dermoscopic features of onychomycosis.…”

“…Five studies reported dermoscopic features of 148 cases of fungal melanonychia ( Table 3 ) ( 29 – 31 , 33 ). These cases demonstrated longitudinal white or yellow streaks (52, 35.1%) ( 31 – 33 ), nail surface scales (39, 33.1%) ( 31 – 33 ) and subungual hyperkeratosis (41, 27.7%) ( 31 – 33 ) ( Table 3 ), which are also common dermoscopic features of onychomycosis. Homogenous pigmentation (75, 50.7%) ( 29 , 30 , 33 ) or longitudinal pigmentation (54, 36.5%) ( 29 , 31 – 33 ) was frequently observed, and the most common colors were multicolor (101, 68.2%) ( 29 – 33 ), brown (84, 56.8%) ( 29 , 31 – 33 ) and black (46, 31.1%) ( 29 , 31 – 33 ).…”

“…These cases demonstrated longitudinal white or yellow streaks (52, 35.1%) ( 31 – 33 ), nail surface scales (39, 33.1%) ( 31 – 33 ) and subungual hyperkeratosis (41, 27.7%) ( 31 – 33 ) ( Table 3 ), which are also common dermoscopic features of onychomycosis. Homogenous pigmentation (75, 50.7%) ( 29 , 30 , 33 ) or longitudinal pigmentation (54, 36.5%) ( 29 , 31 – 33 ) was frequently observed, and the most common colors were multicolor (101, 68.2%) ( 29 – 33 ), brown (84, 56.8%) ( 29 , 31 – 33 ) and black (46, 31.1%) ( 29 , 31 – 33 ). The pigmentation in melanonychia arising from a fungal infection tends to appear brown due to the production of fungal melanin via the pentaketide pathway ( 31 ).…”

“…This is in contrast to melanomas, where melanin is made from tyrosine, and commonly appears as darkly pigmented and black. Findings that appear specific to fungal melanonychia, such as “reverse triangle” (30, 20.3%) ( 30 – 33 ), due to fungal invasion from the distal nail plate and “superficial transverse striation” (41, 27.7%) ( 29 , 30 , 33 ), were also reported. All cases had negative findings for melanoma, such as the lack of the Hutchinson sign (0%) ( 30 – 33 ) and triangular sign (0%) ( 31 , 32 ).…”

Dermoscopy of Onychomycosis: A Systematic Review

“…Dermoscopy can help differentiate onychomycosis from similar conditions including nail psoriasis and traumatic nail dystrophy [3] and can be used to characterize fungal melanonychia [4][5][6][7]. However, the sensitivity and specificity of the dermoscopic signs of onychomycosis are yet to be determined.…”