Diagnosing Porokeratosis of Mibelli Every Time: A Novel Biopsy Technique to Maximize Histopathologic Confirmation

Porokeratosis of Mibelli (PM) is a lesion characterized by a surrounding cornoid lamella with variable nonspecific findings (eg, atrophy, acanthosis, verrucous hyperplasia) in the center of the lesion that typically presents in infancy to early childhood.¹ We report a case of PM in which a prior biopsy from the center of the lesion demonstrated papulosquamous dermatitis. We propose a 3-step technique to ensure proper orientation of a punch biopsy in cases of suspected PM.

Case Report

A 3-year-old girl presented with an erythematous, hypopigmented, scaling plaque on the posterior aspect of the left ankle surrounded by a hard rim. The plaque was first noted at 12 months of age and had slowly enlarged as the patient grew. Six months prior, a biopsy from the center of the lesion performed at another facility demonstrated a papulosquamous dermatitis.

Physical examination revealed a lesion that was 4.2-cm long, 2.2-cm wide at the superior pole, and 3.5-cm wide at the inferior pole (Figure 1). A line was drawn with a skin marker perpendicular to the rim of the lesion (Figure 2A) and a 6-mm punch biopsy was performed, centered at the intersection of the drawn line and the cornoid lamella (Figure 2B). The tissue was then bisected at the bedside along the skin marker line with a #15 blade (Figure 2C) and submitted in formalin for histologic processing. Histologic examination revealed an invagination of the epidermis producing a tier of parakeratotic cells with its apex pointed away from the center of the lesion. Dyskeratotic cells were noted at the base of the parakeratosis (Figure 3). Verrucous hyperplasia was present in the central portion of the specimen adjacent to the cornoid lamella. Based on these histopathologic findings, the correct diagnosis of PM was made.

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.

Porokeratosis of Mibelli (PM) is a lesion characterized by a surrounding cornoid lamella with variable nonspecific findings (eg, atrophy, acanthosis, verrucous hyperplasia) in the center of the lesion that typically presents in infancy to early childhood.¹ We report a case of PM in which a prior biopsy from the center of the lesion demonstrated papulosquamous dermatitis. We propose a 3-step technique to ensure proper orientation of a punch biopsy in cases of suspected PM.

Case Report

A 3-year-old girl presented with an erythematous, hypopigmented, scaling plaque on the posterior aspect of the left ankle surrounded by a hard rim. The plaque was first noted at 12 months of age and had slowly enlarged as the patient grew. Six months prior, a biopsy from the center of the lesion performed at another facility demonstrated a papulosquamous dermatitis.

Physical examination revealed a lesion that was 4.2-cm long, 2.2-cm wide at the superior pole, and 3.5-cm wide at the inferior pole (Figure 1). A line was drawn with a skin marker perpendicular to the rim of the lesion (Figure 2A) and a 6-mm punch biopsy was performed, centered at the intersection of the drawn line and the cornoid lamella (Figure 2B). The tissue was then bisected at the bedside along the skin marker line with a #15 blade (Figure 2C) and submitted in formalin for histologic processing. Histologic examination revealed an invagination of the epidermis producing a tier of parakeratotic cells with its apex pointed away from the center of the lesion. Dyskeratotic cells were noted at the base of the parakeratosis (Figure 3). Verrucous hyperplasia was present in the central portion of the specimen adjacent to the cornoid lamella. Based on these histopathologic findings, the correct diagnosis of PM was made.

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.

Porokeratosis of Mibelli (PM) is a lesion characterized by a surrounding cornoid lamella with variable nonspecific findings (eg, atrophy, acanthosis, verrucous hyperplasia) in the center of the lesion that typically presents in infancy to early childhood.¹ We report a case of PM in which a prior biopsy from the center of the lesion demonstrated papulosquamous dermatitis. We propose a 3-step technique to ensure proper orientation of a punch biopsy in cases of suspected PM.

Case Report

A 3-year-old girl presented with an erythematous, hypopigmented, scaling plaque on the posterior aspect of the left ankle surrounded by a hard rim. The plaque was first noted at 12 months of age and had slowly enlarged as the patient grew. Six months prior, a biopsy from the center of the lesion performed at another facility demonstrated a papulosquamous dermatitis.

Physical examination revealed a lesion that was 4.2-cm long, 2.2-cm wide at the superior pole, and 3.5-cm wide at the inferior pole (Figure 1). A line was drawn with a skin marker perpendicular to the rim of the lesion (Figure 2A) and a 6-mm punch biopsy was performed, centered at the intersection of the drawn line and the cornoid lamella (Figure 2B). The tissue was then bisected at the bedside along the skin marker line with a #15 blade (Figure 2C) and submitted in formalin for histologic processing. Histologic examination revealed an invagination of the epidermis producing a tier of parakeratotic cells with its apex pointed away from the center of the lesion. Dyskeratotic cells were noted at the base of the parakeratosis (Figure 3). Verrucous hyperplasia was present in the central portion of the specimen adjacent to the cornoid lamella. Based on these histopathologic findings, the correct diagnosis of PM was made.

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.