Porokeratosis of Mibelli and superficial disseminated porokeratosis

To the Editor, Although porokeratosis (PK) is an uncommon and poorly understood disorder, diagnosis can be easily achieved on the basis of the clinical picture (annular plaques with a surrounding raised horny border that spreads centrifugally) and a histopathologic hallmark (the cornoid lamella’). Since its first description by Mibelli andRespighi in 1893, a bewildering number of PK types and morphological forms have been reported, resulting in several differing classifications. According to that by Schamroth et al., PK types can be divided clinically into localized forms of Mibelli, including classic (or plaque-type), linear and punctate and disseminated forms, including disseminated superficial PK, disseminated superficial actinic PK and PK palmaris, plantaris et disseminata. Localized forms typically feature fewacral papules that slowlyenlarge in a centrifugal fashion till becoming a prominent plaque with an atrophic center and a raised, M’-shaped section border. Instead, disseminate forms are characterized by many papules scattered on large cutaneous areas and enlarging to superficial and annular plaques with a thin border. A 58-year-old, otherwise healthy Caucasian female was referred with a 20-year history of slowly enlarging and symptomless lesions. Familial history was positive for psoriasis. At physical examination, we observed round-to-oval shaped, atrophic lesions with a slightly raised, erythematous and hyperkeratotic border, varying in size from few millimeters to several centimeters. They were often grouped, sometimes confluent to form small clusters, grossly symmetrical and localized on the frontal (Fig. 1A) and zygomatic regions, dorsum of the hands (Fig. 1 B) and lateral aspect of the legs (Fig. 1C). Large and irregularly shaped plaques on the lateral aspect of feet were characterized by an atrophic and scaly center and a strongly raised border with an apical furrow (Fig. 2A,B). Furthermore, yellowish and uniformly hyperkeratotic oval-shaped plaques, also featuring a strongly raised border, were appreciable on the soles (Fig. 2C). A biopsy specimen was taken from the border of a leg lesion. Histopathological examination featured the cornoid lamella (Fig. 1D), a finding that confirmed the clinical diagnosis of PK. Cycles of topical retinoids were poorly effective, and the patient has been addressed to a long-term clinical follow up. PK types are thought to be the phenotypic expression of a common genetic disorder that may be inherited as an autosomal dominant trait with partial penetrance or result from somatic mutations; recently, disease loci for superficial disseminated actinic PK and superficial disseminated PK were identified. The genetic defect probably determines the presence of abnormal clones of epidermal cells that may proliferate spontaneously or in response to trigger factors such as irradiation, trauma and immunosuppression. The variable age of onset, the many clinical variants and the frequent malignant transformation probably depend on the multifactorial etiopathogenesis of PK. The clinical picture of the case reported here presented features consistent with more than one PK type. In fact, some lesions were roundish and slightly raised and were scattered on the legs, dorsum of hands and face. The morphology was thus typical of superficial PK, and the absence of an evident photodistribution was consistent with a diagnosis of disseminated superficial PK. However, the symmetrical lesions on the lateral aspect of feet and on soles were prominent with a sharply raised border. PK palmaris, plantaris et disseminata, was excluded because of the absence of palmar involvement and the morphology of plantar lesions that were characterized by a sharply raised border. Thus, the more appropriate diagnosis seemed to be that of PK of Mibelli. Reported cases of mixed PK types, mostly involving disseminated superficial actinic PK and linear PK, affected either individuals or families. Only three cases of PK of Mibelli were described in association with another PK type, i.e.