Onychoscopy in pachyonychia congenita: A case series

INTRODUCTION

Pachyonychia congenita (PC) is a rare autosomal-dominant disorder of keratinisation characterised by nail dystrophy, painful palmoplantar keratoderma, oral leucokeratoses, steatocystomas and follicular keratoses. These clinical manifestations are present to varying degrees based on the specific keratin gene mutation causing the disease: KRT6A, KRT6B, KRT6C, KRT16 or KRT17.^[1] Nail involvement can be extensive and involve all 20 nails. The nail changes in PC may be easily misdiagnosed clinically as onychomycosis or psoriasis, and managed inappropriately.

Onychoscopy (dermoscopy of nail) is a non-invasive diagnostic tool that enhances the visualisation of subsurface nail structures and has been increasingly utilised in the evaluation of nail disorders. However, to date, the onychoscopic characteristics of nail involvement in PC have not been well described in the literature. Understanding the specific onychooscopic patterns associated with PC could aid in early recognition, accurate diagnosis and avoidance of unnecessary treatments.

We present clinical, onychoscopic and laboratory assessment of three cases of PC, presenting to our outpatient department. The report aims to highlight the clinical variability of PC and, more importantly, to provide insight into the onychoscopic features of nail dystrophy in PC, thereby contributing to the existing diagnostic framework for this rare genodermatosis.

CASE 1

A 28-year-old male presented with asymptomatic thickening of all 20 nails since birth [Figures 1a and b]. He was born of a consanguineous marriage. There was no history of similar complaints in any family members. The patient also reported excessive sweating of the palms and soles, along with localised thickening of the skin over the bilateral palms. On examination, oral leucokeratosis and focal hyperkeratotic plaques [Figure 1c] over both palms were observed.

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Figure 1: Case 1: (a) Involvement of all 20 nails, (b) thickening of finger nails, (c) focal hyperkeratosis on palms.

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CASE 2

An 11-year-old female presented with progressive thickening of both fingernails and toenails [Figures 2a and b], associated with occasional pain and swelling of the nails. Initially, only a single nail was involved, but over time, the condition progressed to involve all 20 nails. Examination of the oral cavity, palms and soles was unremarkable.

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Figure 2: Case 2: (a) Thickening of all finger nails, (b) Onychogryphosis in left fourth toe.

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CASE 3

An 18-year-old male presented with progressive thickening of multiple fingernails and toenails since early childhood [Figures 3a and b]. There was no history of parental consanguinity, and no similar complaints were reported among family members. Examination of the oral cavity, palms and soles revealed no abnormalities. The patient had no associated cutaneous, dental or mucosal findings. Systemic examination was within normal limits in all three cases. Potassium hydroxide preparation of nail clippings was negative for fungal elements and all three patients underwent histopathological evaluation for confirmation of diagnosis and ruling out differentials. A summary of the clinical and onychoscopic findings is provided in Table 1, with onychoscopy further enhancing the clinical assessment by highlighting subtle nail changes not easily appreciated on gross examination.

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Figure 3: Case 3: (a) Thickening of multiple finger and toe nails, (b) thickening of multiple finger nails.

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Figure 4: Case 1: (a) Onychoscopic evaluation showing obliteration of lunula (blue star), pale appearance of proximal nail plate and brownish appearance of distal nail plate (blue arrow). (b) Compact yellowish brown subungual hyperkeratosis (blue dot). (×10, Polarised mode).

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Figure 5: Case 2: (a) Thickening of nail plate with obliteration of lunula and distal onychorrhexis (blue arrow). (b) Onychogryphosisin the left fourth toe (blue dot). (×10, Polarised mode).

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Figure 6: Case 3: (a) Onychoscopic image showing obliteration of lunula and white thickened nail plate, (b) anonychia in right index finger, (c) pincer nail formation in left ring finger. (×10, Polarised mode).

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DISCUSSION

PC is an uncommon genodermatosis associated with disorder of keratinisation, often presenting with significant nail dystrophy that severely impacts patients’ quality of life. In this report, we describe the onychoscopic findings observed in three patients with clinically and histopathologically diagnosed PC. Given the rarity of this condition and the limited data available in current literature, our observations contribute valuable insights into the onychoscopic characteristics of PC. Onychoscopy, as a non-invasive and accessible diagnostic tool, plays an increasingly important role in the assessment of nail disorders. It enables detailed visualisation of nail plate, bed and periungual structures that may not be appreciated on clinical examination alone. In the context of

PC, onychoscopy can reveal distinctive features that aid early diagnosis and help distinguish PC from close differentials such as psoriasis, onychomycosis or trauma-induced nail changes. Although compact subungual hyperkeratosis may also be seen in psoriatic nails, the absence of nail pitting, a reddish-orange margin of onycholysis and splinter haemorrhages favours a diagnosis of PC. Similarly, while both onychomycosis and PC may present with nail plate thickening and yellow–brown discolouration, the subungual hyperkeratosis of onychomycosis is typically loose and friable, producing a characteristic “ruin” appearance, which contrasts with the compact, adherent keratosis observed in PC. Recognising these findings promptly can guide targeted genetic evaluation, facilitate earlier intervention and improve patient counselling about prognosis, inheritance patterns and surveillance for associated systemic features.

In our evaluation, several consistent onychoscopic features were noted. These included nail plate thickening, likely accounting for the obliteration of the lunula and the pale appearance of the nail plate. Compact subungual hyperkeratosis was observed in all the three cases. Notably, Case 1 exhibited a gently sloping, tapering distal subungual hyperkeratosis, a finding that may represent a morphological clue in PC but requires further validation. The first two cases demonstrated brownish discolouration of the distal nail plate in the absence of any occupational exposure to discolouring substances, suggesting a possible intrinsic association with the disease. In addition, Case 1 demonstrated severe dystrophy of all 20 nails, a finding that has been associated with keratin 6a mutations in prior studies.^[2] In contrast, Case 2 and Case 3 had milder nail findings, highlighting the phenotypic variability seen in PC.

CONCLUSION

Given the scarcity of published data on onychoscopic features of PC, our report adds to the growing body of evidence. Early identification of these features may prevent misdiagnosis and inappropriate treatment. Onychoscopy is not a direct tool for genetic analysis or counselling itself, but it can be used to identify specific nail unit features associated with certain genetic disorders or systemic conditions with a genetic basis such as epidermolysis bullosa, PC, nail patella syndrome and Darier disease. The consistent combination of obliteration of lunula, marked nail plate thickening, pale discolouration of nail plate and subungual hyperkeratosis was observed in our case series. However, larger studies are required to establish hallmark onychoscopic features and their correlation with specific genetic subtypes.