Porokeratosis of the Nail Unit: Case Series and Review

• Nail compromise in porokeratosis is rarely described.

• Lesions in published cases include nail ridging, splitting, pterygium, and anonychia.

• Nail dystrophy from porokeratosis results from the occurrence of a scarring process affecting the nail unit similar to the central area of the porokeratotic cutaneous lesion.

• Porokeratotic nail compromise is progressively destructive and tends to cause permanent damage.

The term “porokeratosis” (PK) includes a group of nonrelated, inherited skin disorders that have in common the presence of a cornoid lamella on histopathology. The cornoid lamella consists of a parakeratotic column overlying a small vertical zone of dyskeratotic and vacuolated cells within the epidermis accompanying a focal loss of the granular layer [1]. The cornoid lamella represents the clinically visible raised margin of lesions of PK. More common types of PK include PK of Mibelli, disseminated superficial PK, segmental (linear) PK, eccrine ostial duct PK, and localized, nonsegmental PK (single lesion PK). Rarer forms have been described [1].

The classic clinical lesions of PK consist of slowing enlarging, isolated or confluent plaques with thin, raised, keratotic margins. As lesions grow centrifugally, the inner, central part of the lesion becomes thinned and atrophic. Here, we present 3 new patients with PK who besides their cutaneous lesions also presented PK affecting the nail unit, and review the previously published cases of ungual PK.

Ungual PK is very rarely described [2-12]. All previously reported cases of ungual PK are characterized by chronicity and tendency toward nail apparatus scarring with tendency to destruction of the nail plate.

Nail scarring occurs in clinical situations where the nail matrix or the nail bed is irreversibly damaged. Clinically, nail scaring ranges from mild (nail plate ridging) to intermediate (splitting), and severe (pterygium and anonychia). The commonest causes of nail scarring include lichen planus (LP) and severe trauma. Rarer causes include other scarring dermatoses such as discoid lupus erythematosus, graft versus host disease, mycosis fungoides, acquired epidermolysis bullosa, epidermolysis bullosa dystrophica, toxic epidermal necrolysis, dyskeratosis congenita, and, very rarely, PK.

A PubMed search (“nail + porokeratosis”) revealed only 11 reports of single patients. The features of these published cases are included on Table 1.

Types of PK involved in these previously reported patients included single lesion PK (1 case), segmental (linear) PK (4), acral or more widespread PK of Mibelli (4), and eccrine ostial duct PK (1). Superficial forms of PK (actinic PK and disseminated superficial PK [1]) are not known to affect the nails. In all reported cases, an advancing cutaneous lesion of PF reached the nail unit, leading to progressive destruction of this structure. Clinical nail compromise included increasing forms of increased severity of nail scarring and destruction: ridging, longitudinal splitting, pterygium, and anonychia. In all patients, histopathological confirmation was obtained. In all cases, attempts to treatment completely failed.

This is the first published case series of ungual PK (Table 2). These 3 new patients presented typical nail scarring due to the poroketatotic process (Fig. 1). Patients 1 and 2 presented intermediate nail destruction characterized by ridging and splitting. They had typical PK of Mibelli, presenting lesions on the limbs that were not limited to the extremities (Fig. 1a, b). Patient 3 had a congenital, segmental lesion of PK that affected the inner right thigh, leg, and dorsum of the foot (Fig. 1c). Pterygium of the first and second toenails resulted from PK compromise of these areas. Histopathology of biopsied keratotic edges of lesions in the 3 patients confirmed the diagnosis of PK (Fig. 2). Longitudinal nail biopsies were not obtained, given the presence of many typical lesions elsewhere, where simple punch biopsies were more easily performed.

Squamous cell carcinomas (SCC) can arise at areas of chronic and intense scarring such as burns, morphea, discoid lupus erythematosus, LP, lupus vulgaris, epidermolysis bullosa dystrophica, hidradenitis, nonhealing ulcers, and, very rarely rarely, PK [13]. These diseases should not be considered “pre-malignant,” nonetheless SCC truly can arise in their chronic scars (Marjolin’s ulcer) [1, 13]. In theory, then, SCC can occur in a cicatricial anonychia due to PK. No such case has been reported so far, probably due to the extreme rarity of ungual PK. The occurrence of SCC in scars of ungual LP (a rare complication of a much more common entity) has been recently reviewed [13].

Nail compromise due to PK results from the occurrence of PK lesions in the vicinity. The centrifugal expansion of such lesions might affect the nail matrix and bed, resulting in scarring of these areas. Thus, albeit very rare in this location, PK will lead to irreversible nail changes.

All 3 patients have given written informed consent to publish photos and details of their cases. Research was conducted ethically in accordance with the World Medical Association Declaration of Helsinki. Written informed consent was obtained from all the patients involved, for publication of their case series and any accompanying images. Ethical approval was not obtained since this is a retrospective case series.

The authors have no conflicts of interest to declare.

The authors declare that there were no funding sources supporting this study.

T.M.Y.: patient management and writing of the manuscript; T.V.B.G.: writing of the manuscript and literature review, M.M.S.N.: idealization, patient management, and final review.