Linear unilateral basal cell nevus (LUBCN) is a rare hair follicle hamartoma that shows overlapping pathological features of basal cell carcinoma (BCC) and basaloid follicular hamartoma (BFH) 1. Herein, we report a case of LUBCN with comedones presenting with pathological features of BFH.
An 18-year-old male patient presented with a 6-month-duration linear lesion affecting the left side of his trunk in a dermatomal pattern. The lesion was composed of variably sized comedones, surrounded with macular hypopigmented areas. Three small flesh-colored papules were also seen among the comedonal lesions (Fig. 1). Mild skin atrophy was perceived in part of the lesion. Physical examination revealed no palmoplantar pits and no skeletal anomalies. Neither parents nor any family members had a similar condition.
Because of an initial clinical impression of a linear nevus comedonicus, a punch biopsy was taken from the comedonal lesions. Histopathological examination revealed large, keratin-filled, dilated infundibulae overlying malformed follicles. The follicular malformation was in the form of thin anastomosing strands and branching cords of undifferentiated basaloid cells replacing or associating hair follicles in a lattice-like pattern. The strands were vertically oriented perpendicular to the epidermis. Peripheral palisading was perceived in some basaloid strands and the malformed follicles were surrounded with cellular connective tissue stroma (Fig. 2). Another biopsy from one of the flesh-colored papules was requested but the patient did not consent.
The available histopathological features were diagnostic of BFH, and, together with the peculiar clinical presentation, the case was diagnosed as LUBCN with comedones (linear nevoid BFH).
LUBCN with comedones was first described by Carney in 1952 2. A few cases have been reported since the first description. Although most of the reported cases showed onset at birth 2–7, delayed onset of appearance as in our case has been reported 8–10. Comedones were described in many of the reported cases 2,4,5,8. Some cases were reported only with linear arrangement of erythematous/flesh-colored papules with or without hypopigmented macules and atrophic areas and without comedones 11–13.
All reported cases described a pathological picture resembling BCC, which is of a benign nonaggressive behavior. However, it is important to mention that in all reports the biopsy was taken from papular lesions. In our case, papular lesions were not biopsied and the pathological features of the comedonal lesions were identical to those described in BFH 7,10. Similar to our findings, lattice-like structures formed of basaloid cells were seen in continuity with the epidermis in addition to foci indistinguishable from BCC in a case of LUBCN 6. It is believed that considerable clinical and histopathological overlap exists between LUBCN and BFH 1,10. LUBCN can be synonymous with linear nevoid BFH 14. The patient showed no other associated anomalies reported with LUBCN, such as osteoma cutis, anodontia, abnormal bone mineralization, or scoliosis 9.
The most important differential diagnosis in this context is the unilateral nevoid basal cell carcinoma syndrome (NBCCS) 15–17. In such cases the patients show, in addition to the multiple unilateral BCCs (with aggressive clinical behavior), classic features of NBCCS, such as skeletal anomalies, jaw cysts, palmoplantar pits, facial dysmorphism, and calcifications of the falx cerebri, and do not show comedones, hypopigmented macules, or atrophic areas. The lack of loss of heterozygosity at the PTCH locus, lack of inactivating patched (PTCH) mutations, and the lack of activating SMO (Smoothened, Frizzled Class Receptor) gene mutations would have provided additional evidence to favor LUBCN over unilateral nevoid basal cell carcinoma syndrome 13; however, these techniques are not available in our country.
The clinical behavior in LUBCN is benign and the treatment of the lesions is only for cosmetic purposes. However, as this lesion is believed to be analogous to epidermal nevus syndrome, based on some associated anomalies 9, and because of previous reports on the development of BCC in epidermal nevi 18, follow-up of patients with LUBCN is needed.
Conflicts of interest
There are no conflicts of interest.
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