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HJ Kim, et al
460
Ann Dermatol
Received June 3, 2019, Revised May 22, 2020, Accepted for publication
May 22, 2020
Corresponding author: Hyun-Chang Ko, Department of Dermatology, Pusan
National University Yangsan Hospital, 20 Geumo-ro, Mulgeum-eup, Yangsan
50612, Korea. Tel: 82-55-360-1678, Fax: 82-55-360-1679, E-mail: hcko@
pusan.ac.kr
ORCID: https://orcid.org/0000-0002-3459-5474
T
his is an Open Access article distributed under the terms of the Creative
Commons Attribution Non-Commercial License (http://creativecommons.
org/licenses/by-nc/4.0) which permits unrestricted non-commercial use,
distribution, and reproduction in any medium, provided the original work
is properly cited.
Copyright © The Korean Dermatological Association and The Korean
Society for Investigative Dermatology
pISSN 1013-9087ㆍeISSN 2005-3894
Ann Dermatol Vol. 32, No. 6, 2020 https://doi.org/10.5021/ad.2020.32.6.460
ORIGINAL ARTICLE
Clinical and Dermoscopic Features of Fungal
Melanonychia: Differentiating from Subungual
Melanoma
Hak-Jun Kim1,2, Tae-Wook Kim1,2, Sung-Min Park1,2, Hyun-Joo Lee1, Gun-Wook Kim1,
Hoon-Soo Kim1, Byung-Soo Kim1, Moon-Bum Kim1, Hyun-Chang Ko1,2
1Department of Dermatology, Pusan National University Hospital, Busan, 2Department of Dermatology, Pusan National University
Yangsan Hospital, Yangsan, Korea
Background: Fungal melanonychia (FM) is a rare nail dis-
order that presents as dark pigmentation in the nail plate be-
cause of fungal nail infection. The diagnosis of FM is occa-
sionally confusing because its appearance is similar to mela-
nonychia due to other causes including malignant melanoma.
Dermoscopy could help increase the accuracy of diagnosing
the cause of pigmented nail lesions. However, dermoscopic
features of FM are not well elucidated. Objective: This study
aimed to investigate clinical and dermoscopic character-
istics of FM. Methods: The clinical features and dermoscopic
findings of 20 patients diagnosed with FM and 14 patients di-
agnosed with subungual melanoma the Department of
Dermatology of Pusan National University Hospitals (Busan
and Yangsan) were retrospectively reviewed. Results: FM
mainly occurred as a solitary form in the toenail. Patients in
the FM group were older than those in the subungual mela-
noma group. The most distinguishable general dermoscopic
features in FM were a distal diffuse pattern, distal linear pat-
tern, and light brown to yellowish color. FM-associated spe-
cific dermoscopic patterns such as the reverse triangular pat-
tern, subungual hyperkeratosis, scale on the nail surface, and
white or yellowish streaks were dominantly observed in the
FM group compared to the subungual melanoma group.
Conclusion: FM-associated dermoscopic patterns and distal
diffuse and linear patterns could be helpful diagnostic clues
for differential diagnosis of FM from subungual melanoma.
(Ann Dermatol 32(6) 460∼465, 2020)
-Keywords-
Dermoscopy, Fungal melanonychia, Subungual melanoma
INTRODUCTION
Fungal melanonychia (FM) is a rare nail disorder that pres-
ents with dark to brown pigmentation due to fungal in-
fection of the nails. It is mainly caused by dematiaceous
fungi and, rarely, by yeasts and non-dermatophyte fungi1.
The diagnosis of FM is occasionally difficult because it
may clinically mimic melanonychia due to other causes,
such as melanocytic nevus and subungual melanoma.
Recently, dermoscopy has been used to improve the accu-
racy of diagnosing the cause of pigmented nail lesions. A
few studies have evaluated the dermoscopic features of
FM2,3. However, these studies were limited by a small
sample size or the absence of control groups. Here, we
aimed to identify the clinical and dermoscopic character-
istics of FM to enhance the accuracy of diagnosis. In this
study, we have compared clinical and dermoscopic fea-
tures of FM with those of subungual melanoma.
Characteristic Features of Fungal Melanonychia
Vol. 32, No. 6, 2020
461
Fig. 1. The general shapes of mela-
nonychia that were analyzed in this
study; (A) longitudinal, (B) distal li-
near, (C) total diffuse, and (D) distal
diffuse pattern.
MATERIALS AND METHODS
Study population
Of the patients with FM who visited the Department of
Dermatology of Pusan National University Hospitals (Busan
and Yangsan), South Korea from December 2014 to August
2018, a total of 20 patients who had dermoscopic records
were included in this study. The diagnosis of FM was made
based on clinical presentations and a mycological test. A
potassium hydroxide (KOH) smear test was performed in
all patients, and only patients with positive test results were
enrolled. Fungal culture was not always performed because
of its low sensitivity and long incubation period. The con-
trol group comprised all patients diagnosed with subun-
gual melanoma with dermoscopic records during the same
period. Subungual melanoma was diagnosed by histopatho-
logical findings. Of the 14 patients who had subungual
melanoma, 4 had invasive melanoma. All subungual mel-
anomas were confirmed by a negative KOH smear test and
excluded accompanying fungal infection. The study was
exempted from the requirement for approval by the ethics
committee of Pusan National University Yangsan Hospital
(IRB no. 05-2019-057), and informed consent was obtained
from the patients included in this study.
We received the patient’s consent form about publishing
all photographic materials.
Method
Data from the medical records of patients were used to in-
vestigate the clinical characteristics of the patients (age,
sex, number of lesions, location, involved area, duration,
and comorbidities). Clinical photographs were taken with
a camera (EOS 50D; Canon, Tokyo, Japan). Dermoscopic
images were acquired using a dermoscope (DermLite II
PRO HR or DermLite II DL3; 3Gen, San Juan Capistrano,
CA, USA) that was equipped with a digital camera (CyberShot
DSC W-290; Sony Co, Tokyo, Japan).
All data were analyzed using IBM SPSS Statistics ver. 22.0
(IBM Corp., Armonk, NY, USA). p-values of less than 0.05
were considered significant.
Evaluation of dermoscopic features
General dermoscopic features (color and general shape)
were investigated. The color of the nail lesion was divided
into black, dark brown, light brown, yellow, gray, and red
categories. The general shape of the melanonychia was clas-
sified as longitudinal, distal diffuse, proximal diffuse, distal
linear, and total diffuse patterns (Fig. 1). FM-associated der-
moscopic patterns, including reverse triangular shapes, sub-
ungual hyperkeratosis, scales on the nail surfaces, and yel-
HJ Kim, et al
462
Ann Dermatol
Fig. 2. The fungal melanonychia-
associated dermoscopic patterns. (A)
Reverse triangular shape (yellow
asterisks), (B) subungual hyperkera-
tosis (whitish arrow), (C) scales on
the nail surface (red arrows), and
(D) yellowish streaks (yellow circle).
Table 1. Sociodemographic and clinical features of fungal
melanonychia (FM group) and subungual melanoma (control
group)
Feature FM group
(n=20)
Control group
(n=14) p-value
Age of onset (yr) 57.2 (30~87) 55.1 (42~78) ＜0.05
Sex
Male 10 6 0.062
Female 10 8
Location
Finger:toe 6:16 9:5 ＜0.05
Right:left 11:9 8:6 0.133
Mean no. of
nails involved
1.1 1.0 0.674
Involved area (%) 27.3 38.7 ＜0.05
Duration (mo) 18.2 20.8 0.088
Comorbidity
Hypertension 9 8
Diabetes 7 6
Dyslipidemia 4 5
Cancer 3 3
Others 2 3
Values are presented as mean (range) or number only.
lowish streaks, were evaluated (Fig. 2). Melanoma-asso-
ciated patterns, such as Hutchinson’s nail sign, irregularity,
nail plate destruction, the triangular sign, and ulceration,
were also evaluated to find a diagnostic clue that differ-
entiates FM from subungual melanoma.
RESULTS
Sociodemographic and clinical features
The sociodemographic and clinical information of the FM
and control groups (the subungual melanoma group) are
presented in Table 1. We reviewed 34 patients (20 pa-
tients with FM and 14 patients with subungual melano-
ma). The mean age was 57.2 and 55.1 years in the FM
and the subungual melanoma groups, respectively. The
male-to-female ratio was 1:1 and 1:1.8 in the FM and sub-
ungual melanoma groups, respectively. FM occurred on
1.1 nail units per patient, and subungual melanoma oc-
curred on 1.0 nail units per patient. The involved nail area
of the FM group was smaller than that of the control group
(27.3% in FM, 38.7% in subungual melanoma, p＜0.05).
There was no significant difference in incidence rates be-
tween the left side and the right side of the body. FM oc-
curred in the toenails three times more often than in the
Characteristic Features of Fungal Melanonychia
Vol. 32, No. 6, 2020
463
Table 2. General dermoscopic features of fungal melanonychia
(FM group) and subungual melanoma (control group)
General dermo-
scopic feature
FM group
(n=20)
Control group
(n=14) p-value
Color
Black 10 (50.0) 6 (42.9) 0.231
Dark brown 9 (45.0) 8 (57.1) 0.177
Light brown 9 (45.0) 0 (0) ＜0.05
Yellow 8 (40.0) 0 (0) ＜0.05
Gray 0 (0) 0 (0) -
Red 0 (0) 0 (0) -
Multicolored
pattern
(＞2 colors)
13 (65.0) 11 (78.6) 0.159
General pattern
Longitudinal 6 (30.0) 6 (42.9) 0.056
Distal diffuse 7 (35.0) 0 (0) ＜0.05
Proximal diffuse 1 (5.0) 2 (14.3) 0.088
Distal linear 4 (20.0) 0 (0) ＜0.05
Total diffuse 2 (10.0) 5 (35.7) ＜0.05
Values are presented as number (%). -: not available.
Table 3. Specific dermoscopic features of fungal melanonychia
(FM group) and subungual melanoma (control group)
Specific dermo-
scopic feature
FM group
(n=20)
Control group
(n=14) p-value
FM associated pattern
Reverse
triangular shape
10 (50.0) 0 (0) ＜0.05
Subungual
hyperkeratosis
7 (35.0) 2 (14.3) ＜0.05
Scales on
the nail surface
14 (70.0) 8 (57.1) ＜0.05
White or
yellow streak
18 (90.0) 0 (0) ＜0.05
MM associated pattern
Hutchinson sign 0 (0) 8 (57.1) ＜0.05
Pseudo-Hutchins
on sign
0 (0) 4 (28.6) ＜0.05
Nail plate
destruction
5 (25.0) 4 (28.6) 0.312
Triangular sign 0 (0) 5 (35.7) ＜0.05
Dots/globules 4 (20.0) 7 (50.0) ＜0.05
Ulceration 0 (0) 2 (14.3) ＜0.05
Values are presented as number (%). MM: malignant melanoma.
fingernails. The most common onset site of FM was the
first toe (55.0%), followed by the first finger (15.0%), and
the second toe (10.0%). In contrast, subungual melanoma
nail lesions were found predominantly in the fingernails
and mainly occurred in the second finger (35.7%), first fin-
ger (28.6%), and first toe (14.3%). There was no signifi-
cant difference in the disease duration between the two
groups. Hypertension was the most common comorbidity
in both groups, followed by diabetes and dyslipidemia.
Dermoscopic features
The general dermoscopic characteristics, such as color and
shape of the melanonychia, are summarized in Table 2. In
the FM group, the most common color was black (50.0%),
followed by dark brown (45.0%), light brown (45.0%),
and yellow (40.0%). In the control group, the most com-
mon colors were dark brown (57.1%) and black (42.9%).
Although black and dark brown were the predominant
colors in both groups, the proportion of yellow melano-
nychia was significantly higher in the FM group than in
the control group (40.0% vs. 0%). The most common FM
pattern was a distal diffuse type of melanonychia (35.0%).
Other common patterns included the longitudinal (30.0%),
distal linear (20.0%), and total diffuse (10.0%) types of
melanonychia. Among these, the distal diffuse and linear
patterns were more distinctive in the FM group than in the
control group (p＜0.05). Statistical analyses between the
FM and subungual melanoma groups were performed to
identify specific dermoscopic differences (Table 3). We
analyzed the following four FM-associated dermoscopic
patterns: white or yellow streaks, reverse triangular pat-
terns, subungual hyperkeratosis, and scales on the nail
surfaces. In this study, we observed that all four features
were positive predictors of FM (Fig. 2). In contrast, mela-
noma-associated patterns, such as Hutchinson’s sign, pseudo-
Hutchinson’s sign, the triangular sign, nail plate destruc-
tion, dots/globules, and ulceration, were negative predictors
of FM compared with the subungual melanoma (p＜0.05).
DISCUSSION
Melanonychia is defined by dark pigmentations in the nail
unit. There are many different causes of melanonychia,
ranging from nail matrix nevus, melanocytic activation due
to drug use or trauma, subungual hemorrhage, and infec-
tion to malignant melanoma. Some of these causes have
unique presentations, which make them easy to distinguish.
However, most cases of melanonychia are difficult to dis-
tinguish because of their similar clinical presentations4,5.
FM is a rare nail disorder that presents with dark to brown
pigmentation on the nail plate because of fungal nail
infection. Some species of fungi can synthesize melanin.
Unlike human melanin, which is derived from tyrosine,
fungal melanin is synthesized via the pentaketide pathway.
The fungal melanin serves as a barrier that protects the
fungus from environmental stresses, such as temperature,
HJ Kim, et al
464
Ann Dermatol
radiation, and the host’s immune system. In addition, mel-
anin-synthesizing fungi are more resistant to ultraviolet
and X-ray radiation and extreme temperatures compared
to other fungi. Among the many species of fungi, the most
frequently isolated fungi in FM are Trichophyton rubrum,
a nondematiaceous dermatophyte, and Scytalidium dimi-
diatum, a dematiaceous fungi1,6. However, no analysis
was made about causative organisms in this study because
fungal culture was not routinely performed. Further stud-
ies will be needed to investigate characteristic patterns of
FM based on specific causative pathogens.
We compared the clinical and dermoscopic features of
FM with subungual melanoma to find diagnostic differ-
ences between the groups. The clinical features showed
that the onset age of FM was relative older than that of the
control. The mean age of FM was 57.2 years, which was
significantly higher than that of individuals in the control
group (55.1 years). FM showed a tendency to develop in a
single nail unit (1.1 nail units per patients). However,
some patients with a solitary FM lesion had multiple nail
unit (mean 3.67) involvement of onychomycosis. In a
study of 1897 Korean patients with onychomycosis, 31.3%
of patients showed multiple nail involvement (i.e., more
than 5 nail units involved)7. In contrast, multiple nail in-
volvement of FM was rarely observed in this study, with
only one patient showing FM of multiple nails. This sug-
gested that the incidence of FM is relatively low compared
to onychomycosis. Furthermore, in previous studies, most
cases of onychomycosis (93.8%) involved toenails, and
only 2.2% of the cases involved fingernails7. Similarly, FM
occurred three times more often in toenails (72.7%) than
in fingernails (27.2%) in this study. However, subungual
melanoma was mainly observed in fingernails (64.3%). To
summarize the clinical analysis, FM tends to occur as a
solitary lesion in the great toe, and its mean age of onset
was higher than in cases of subungual melanoma.
Dermoscopy is a useful noninvasive tool that has been re-
ported to improve diagnostic accuracy of nail pigmentation.
Reports on the dermoscopic features of FM are scarce, and
only a few original studies on FM have been reported2,8.
Kilinc Karaarslan et al.3 have described the dermoscopic
patterns in 14 cases of FM and suggested that multicolored
pigmentation and reverse triangular patterns are distinctive
features of FM. Hirata et al.9 have also reported a case of
FM; they dermoscopically described it as a brown nail
background with regular black lines. However, these stud-
ies were limited by a small sample size and the absence of
a control group. Ohn et al.2 have reported the first com-
prehensive comparative analysis of dermoscopic findings
between FM and other melanonychia caused by nail ma-
trix nevus, melanocytic activation, and subungual melanoma.
Their study revealed that several dermoscopic features,
such as reverse triangular patterns, subungual hyper-
keratosis, and white or yellow streaks, were characteristics
of FM. In this study, we observed that all these patterns
were predominantly observed in FM cases. Among these
patterns, white or yellow streaks and reverse triangular pat-
terns were the most distinctive features of FM. Black pig-
mentation was the predominant color in the control group.
This study also showed that the yellow color was a pos-
itive indicator for FM. Ohn et al.2 suggested that multi-
colored patterns were characteristic of FM. However, this
study showed no significant difference in the presence of
multicolored patterns between the FM and control groups.
We chose cases of subungual melanoma as the control
group because it usually has a heterogenous clinical pre-
sentation. The most common general pattern of dermo-
scopic findings in FM was the distal diffuse pattern (35.0%),
followed by the longitudinal (30.0%) and distal linear (20.0%)
patterns. The two distal patterns were indicators of FM (p＜
0.05), but the longitudinal pattern was not. The longitudi-
nal pattern was the predominant pattern in the control
group (42.9%). Two distal patterns that were not presented
in the previous report were identified as characteristic FM
dermoscopic findings in this study.
Piraccini et al.10 have reported that irregular white to yel-
low pigmentation and a “jagged edge” with sharp longi-
tudinal whitish indentations are specific features of FM. In
some previous studies, the spike or streak were useful in-
dicators of fungal invasion of the nail plate. In this study,
we used the term “white or yellow streak,” and this pat-
tern was more frequently observed in the FM group (90.0%)
than in the control group (0%). The reverse triangular pat-
tern is caused by fungal invasion from the distal nail
plate11, and our data showed that this pattern was preva-
lent in the FM group (50.0%), but not in the melanoma
group (0%).
Subungual melanoma should always be included in the
differential diagnosis of FM because melanoma is a life-
threatening disorder. FM could mimic subungual melano-
ma because it can present as a brown-black melanonychia
with a heterogenous pattern12,13. We observed that mela-
noma-associated features aid in distinguishing between
FM and subungual melanoma. The clinical diagnosis should
be supported by dermoscopy findings as it may be benefi-
cial if a biopsy or mycologic examination of the lesions is
required. There are some limitations to this study. Since
differential diagnosis of FM from malignant melanoma is
important in cases of pigmented lesions of the nail units,
especially in melanonychia of the elderly, histopathologic
evaluation is essential for an accurate diagnosis. However,
patients with FM in this study were diagnosed based on
Characteristic Features of Fungal Melanonychia
Vol. 32, No. 6, 2020
465
clinical findings and KOH smear tests only. This study has
a retrospective design and a small number of patients;
therefore, a prospective study with a larger scale is needed.
However, this study is meaningful as it compares not only
general dermoscopic patterns but also each specific der-
moscopic feature between rare FM and subungual mela-
noma, which is the most important discriminating disease.
In conclusion, we suggest that two general dermoscopic
patterns (distal diffuse and linear) and FM-associated spe-
cific dermoscopic patterns can be used as diagnostic clue
to differentiate FM from subungual melanoma. In the fu-
ture, it is necessary to confirm the results through large-
scale follow-up studies.
CONFLICTS OF INTEREST
The authors have nothing to disclose.
FUNDING SOURCE
This work was supported by a 2-year Research Grant of
Pusan National University.
DATA SHARING STATEMENT
The data that support the findings of this study are avail-
able from the corresponding author upon reasonable re-
quest.
ORCID
Hak-Jun Kim, https://orcid.org/0000-0003-1723-4244
Tae-Wook Kim, https://orcid.org/0000-0001-8922-8754
Sung-Min Park, https://orcid.org/0000-0002-4915-8111
Hyun-Joo Lee, https://orcid.org/0000-0002-1088-0975
Gun-Wook Kim, https://orcid.org/0000-0003-1599-7045
Hoon-Soo Kim, https://orcid.org/0000-0002-7649-1446
Byung-Soo Kim, https://orcid.org/0000-0003-0054-8570
Moon-Bum Kim, https://orcid.org/0000-0003-4837-0214
Hyun-Chang Ko, https://orcid.org/0000-0002-3459-5474
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