Dear Editor, Onychomatricoma (OM), first described by Baran and Kint,[1] is considered a rare benign tumour of the nail matrix with no more than 80 cases reported in the literature. The fingernails of white adult patients are most commonly affected. Reported clinical features include localized or diffuse thickening of the nail plate, transverse overcurvature, xanthonychia, multiple splinter haemorrhages, which often affect the proximal nail plate, and the presence of holes in the distal margin of the nail plate.[2] When the proximal nail fold is reflected and the nail plate is avulsed, OM appears as a villous matrix tumour with projections that penetrate along the length of the thickened nail plate. Differential diagnoses include fibrokeratoma of the nail matrix, onychomycosis, squamous cell carcinoma, Bowen disease, viral warts, nail fibroma and longitudinal melanonychia. Diagnosis can be confirmed with nail clipping[3] and imaging methods including ultrasound,[4] magnetic resonance imaging and confocal microscopy.[5] Histological examination reveals distinctive features that confirm the diagnosis.[2–7] The aim of this study is to collect epidemiological and clinical data of a large series of patients with OM and to compare the findings with previous studies.
The medical records and clinical pictures of 30 patients with OM, diagnosed from 2005 to 2012 by five dermatologists with a special interest in nail disorders, were retrospectively collected and evaluated for epidemiological data and clinical features. All lesions had been surgically removed and the diagnosis was confirmed by pathology. For each case, all clinical manifestations described in previous studies were scored as present or absent.[8–12] Statistical analysis by simple percentage was performed for age, sex, skin photo type, digit and duration.
The clinical features (Figs 1 and 2) and demographic data of the 30 patients identified in this study are summarized below. The relative and absolute frequencies of clinical features are reported in Table 1 .
Figure 1.
Longitudinal thickening, xanthonychia and splinter haemorrhage involving the proximal nail plate.
Figure 2.
Dermoscopy showing splinter haemorrhages involving the proximal and distal nail plate within the band of xanthonychia.
Nineteen tumours (64%) occurred in the fingers (seven in the thumb, three in the second finger, seven in the third finger, two in the fifth finger). Overall, 12 tumours occurred in the dominant hand and 18 in the nondominant hand. Eleven tumours involved the toenails (37%); seven in the big toenail, two in the second toe and two in the third toe.
The observed clinical features ( Table 1 ) were as follows: increased nail thickness (25 of 30 cases; 83%), splinter haemorrhages (24 of 30 cases; 80%) with proximal splinters in four cases and both proximal and distal splinters in another four cases (information about splinter localization was not available for two cases), longitudinal xanthonychia (22 of 30 cases; 73%), increased transverse curvature of the nail (15 of 30 cases; 50%), erythema and swelling at the proximal nail fold (15 of 30 cases; 50%), woodworm-like cavities of the free edge of the nail plate (13 of 30 cases; 43%), pain during nail compression (nine of 30 cases; 30%) and longitudinal melanonychia (seven of 30 cases; 23%) ( Table 1 ). If we consider longitudinal melanonychia as a variant of xanthonychia, the latter was the most common clinical feature occurring in 29 of 30 cases (97%).
The analysis of signs that were seen together for each patient showed that the most common association of clinical features was increased nail thickness, splinter haemorrhages and xanthonychia (16 patients; 53%). Frequently these clinical features were associated with woodworm-like cavities visible to the naked eye (11 patients; 37%) and with increased transverse curvature of the nail (eight patients; 27%). Other combinations were observed, but with lower frequency.
The mean number of clinical features observed in each patient was 4·23. Twenty-four patients (80%) had between three and six clinical features (Fig. 3).
Figure 3.
Number of clinical features per patient.
Features observed during surgical excision of OM, such as filiform projections and cavitations of the proximal part of the nail plate, were not considered as clinical manifestations for analysis in this study.
There was no significant relation between tumour duration and nail thickness, but tumours lasting for more than 5 years were most frequently associated with erythema and swelling of the proximal nail fold. Dermoscopy was performed in 10 cases. The most common dermoscopic features included the presence of longitudinal white lines, proximal and distal splinter haemorrhages and holes in the distal margin (Fig. 2).
OM has been described as a rare tumour of the nail apparatus with its origins in the nail matrix. Diagnosis is based upon clinical aspects, dermoscopy, ultrasound, magnetic resonance imaging and pathology (Fig. 4). Treatment for OM is surgical. Removal of the nail plate permits visualization of the matrix tumour characterized by tufted projections.
Figure 4.
(a) Nail plate in an excisional specimen from onychomatricoma. Note the digitated epithelial proliferations in the nail plate parallel to its longitudinal axis. (b) Nail plate in a nail clipping from onychomatricoma. Note the numerous serum filled cavities showing parakeratotic epithelial lining.
OM predominantly affects women (2·16 : 1), with a peak incidence at around 51 years of age.[4] It is rare in children, with only one case described in the literature.[9] It almost exclusively affects patients with light skin colour. The fingers are more frequently affected than the toes.[10] Similar findings were encountered in our series. The average age of patients was 47·9 years (21–70 years). There was a predominance of OM in the fingers (19 cases in the fingers contrasted with 11 cases in the toes) and a predominance of cases affecting women (the female/male ratio was 1·3 : 1). Nondominant hands were more commonly affected.
The large majority of OM cases were diagnosed in people with light skin (24 cases). There were no cases diagnosed in people with dark brown skin. This finding is relevant given the large percentage of population of African descent found in Brazil and in Miami.
The mean duration of OM was 12·7 years, probably due to a lack of knowledge of the clinical aspects of OM and also due to the fact that the tumour is usually painless.
In our large series of OM the three most common signs were thickening of the nail plate, splinter haemorrhages and xanthonychia (83%, 80% and 73%, respectively). Proximal splinter haemorrhages were observed in four cases. Other common clinical features were transverse overcurvature, erythema and swelling of the proximal nail fold and woodworm-like cavities of the free edge of the nail plate.
Melanonychia was observed in seven cases. The most frequent clinical presentation was the association of nail-plate thickening, splinter haemorrhages and xanthonychia, observed in 53% of patients. Other signs were often present and 24 patients (80%) exhibited between three and six different clinical features. There were no significant correlations between clinical signs and tumour duration except for inflammatory nail-fold signs, which were more common in long-lasting tumours.
Although OM is a characteristic and well-defined nail matrix tumour, diagnosis is often delayed. This may be because dermatologists are not familiar with the clinical features of this tumour. The presence of localized longitudinal thickening and xanthonychia of the nail plate should suggest this diagnosis. Splinter haemorrhages are commonly seen and often affect the proximal nail plate.
The British Journal of Dermatology. 2015;173(5):1305-1307. © 2015 Blackwell Publishing
