eMedicine Specialties > Dermatology > Benign Neoplasms

Porokeratosis: Differential Diagnoses & Workup

Author: Linda V Spencer, MD, Consulting Staff, Department of Dermatology, St Clare Medical Center
Contributor Information and Disclosures

Updated: Aug 3, 2009

Differential Diagnoses

Psoriasis, Plaque

Other Problems to Be Considered

Linear verrucous epidermal nevus
Porokeratotic eccrine ostial and dermal duct nevus

Workup

Laboratory Studies

  • Generally, no laboratory studies are required.
  • Screening for diseases causing immunosuppression (eg, HIV, hematologic malignancies) and/or renal failure is appropriate when new lesions of classic porokeratosis of Mibelli (PM) or disseminated superficial porokeratosis (DSP) are seen or when sudden exacerbation of any form of porokeratosis develops.

Histologic Findings

The cornoid lamella is the histopathologic hallmark of all forms of porokeratosis. It is essential that the specimen be taken from the peripheral, raised, hyperkeratotic ridge to demonstrate this finding.

The cornoid lamella consists of a thin column of tightly packed parakeratotic cells within a keratin-filled epidermal invagination. The parakeratotic column extends at an angle away from the center of the lesion and develops from the interfollicular epidermis, but it may involve the ostia of hair follicles or sweat ducts. Within the parakeratotic column, the horny cells appear homogeneous and possess deeply basophilic pyknotic nuclei. In the epidermis beneath the parakeratotic column, the keratinocytes are irregularly arranged and have pyknotic nuclei with perinuclear edema. No granular layer is seen within the parakeratotic column, while the keratin-filled invagination of the epidermis has a well-developed granular layer. The papillary dermis beneath the cornoid lamella contains a moderately dense, lymphocytic infiltrate and dilated capillaries. Dermal amyloid deposits have been described in some cases of disseminated superficial actinic porokeratosis (DSAP).

Specimens taken from the center of the lesion show atrophy, with areas of liquefaction degeneration in the basal layer, colloid-body formation, and flattening of rete ridges. The dermis may be edematous or fibrotic with telangiectasia. Amyloid deposition may be seen in the papillary dermis, both centrally and beneath the cornoid lamellae. The cornoid lamella is prominent in PM but less distinct in DSAP, DSP, and porokeratosis palmaris et plantaris disseminata (PPPD). At the ultrastructural level, vacuolization of keratinocytes, clumping of keratin filaments, and a paucity of lamellar bodies are found. Intercellular lamellar sheets are incompletely formed and may be responsible for defective desquamation.

Immunohistochemical studies show that keratinocytes beneath the cornoid lamella stain in a pattern similar to that observed in squamous cell carcinomas. The parakeratosis appears to be the result of faulty maturation of keratinocytes, rather than an increased rate of proliferation.18 Keratinocytes central to the cornoid lamella stain in a pattern identical to that of premalignant lesions, such as actinic keratosis. Keratinocytes peripheral to the cornoid lamella stain normally.

More on Porokeratosis

Overview: Porokeratosis
Differential Diagnoses & Workup: Porokeratosis
Treatment & Medication: Porokeratosis
Follow-up: Porokeratosis
Multimedia: Porokeratosis
References
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References

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Further Reading

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Keywords

porokeratosis, classic porokeratosis of Mibelli, PM, disseminated superficial actinic porokeratosis, DSAP, disseminated superficial porokeratosis, DSP, porokeratosis palmaris et plantaris disseminata, PPPD, linear porokeratosis, punctate porokeratosis

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Contributor Information and Disclosures

Author

Linda V Spencer, MD, Consulting Staff, Department of Dermatology, St Clare Medical Center
Linda V Spencer, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, and Indiana State Medical Association
Disclosure: Amgen Grant/research funds Other

Medical Editor

Marjan Garmyn, MD, PhD, Professor, Faculty of Medicine, Katholieke Universiteit Leuven, Belgium; Chair and Adjunct Head, Department of Dermatology, University of Leuven, Belgium
Disclosure: Nothing to disclose.

Pharmacy Editor

Richard P Vinson, MD, Assistant Clinical Professor, Department of Dermatology, Texas Tech University School of Medicine; Consulting Staff, Mountain View Dermatology, PA
Richard P Vinson, MD is a member of the following medical societies: American Academy of Dermatology, Association of Military Dermatologists, Texas Dermatological Society, and Texas Medical Association
Disclosure: Nothing to disclose.

Managing Editor

Jeffrey P Callen, MD, Professor of Medicine, Chief, Division of Dermatology, University of Louisville School of Medicine
Jeffrey P Callen, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American College of Physicians, and American College of Rheumatology
Disclosure: Amgen Honoraria Consulting; Abbott Honoraria Consulting; Electrical Optical Sciences Honoraria Consulting; Centocor Honoraria Consulting; Medicis Honoraria Consulting; Celgene Honoraria Consulting

CME Editor

Catherine Quirk, MD, Clinical Assistant Professor, Department of Dermatology, Brown University
Catherine Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology
Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center
Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

 
 
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