Diagnosing Porokeratosis of Mibelli Every Time: A Novel Biopsy Technique to Maximize Histopathologic Confirmation
Porokeratosis of Mibelli (PM) is a rare condition with the potential for malignant transformation that presents a clinical and pathologic diagnostic challenge. An improperly oriented biopsy may lead to the wrong histopathologic diagnosis. We report a case of PM that was previously misdiagnosed and describe a biopsy technique for suspected PM that maximizes the potential for histopathologic confirmation of the diagnosis.
Practice Points
- A biopsy from the center of a plaque of porokeratosis will produce nonspecific findings.
- Bisecting the punch specimen at the bedside along a line drawn perpendicular to the cornoid lamella guarantees proper orientation of the specimen.
Comment
Porokeratosis of Mibelli is a rare condition that typically presents in infancy to early childhood.1 It may appear as small keratotic papules or larger plaques that reach several centimeters in diameter.2 There is a 7.5% risk for malignant transformation (eg, basal cell carcinoma, squamous cell carcinoma, Bowen disease).3 Variable nonspecific findings (eg, atrophy, acanthosis, verrucous hyperplasia) typically are present in the center of the lesion. In our case, a biopsy from the center of the plaque demonstrated verrucous hyperplasia. The incorrect diagnosis of PM as psoriasis also has been reported.4
We propose a 3-step technique to ensure proper orientation of a punch biopsy in cases of suspected PM. First, draw a line perpendicular to the rim of the lesion to mark the biopsy site (Figure 2A). Second, perform a punch biopsy centered at the intersection of the drawn line and the cornoid lamella (Figure 2B). Third, section the biopsied tissue with a #15 blade along the perpendicular line at the bedside (Figure 2C). The surgical pathology requisition should mention that the specimen has been transected and the cut edges should be placed down in the cassette, ensuring that the cornoid lamella will be present in cross-section on the slides.
If the punch biopsy specimen is not bisected, it can be difficult to orient it in the pathology laboratory, especially if the cornoid lamellae are not prominent. Furthermore, the technician processing the tissue may not be aware of the importance of sectioning the specimen perpendicular to the cornoid lamella. Following this procedure, diagnosis can be confirmed in virtually every case of PM.
