title: Histopathological Differential Diagnosis of Psoriasis and Seborrheic Dermatitis of the Scalp.
abstract: BACKGROUND
  The differential diagnosis of psoriasis and seborrheic dermatitis can be difficult when both conditions are localized to the scalp without the involvement of other skin sites.
  
  
  OBJECTIVE
  We aimed to evaluate the histopathological differences between psoriasis and seborrheic dermatitis on the scalp and identify favorable criteria for their differential diagnosis.
  
  
  METHODS
  We evaluated 15 cases of psoriasis and 20 cases of seborrheic dermatitis of the scalp that had been clinicopathologically diagnosed. Skin biopsy sections stained with H&E were examined. Additional immunohistochemistry was performed, including Ki-67, keratin 10, caspase-5, and GLUT-1.
  
  
  RESULTS
  On histopathological examination, mounds of parakeratosis with neutrophils, spongiform micropustules of Kogoj, and clubbed and evenly elongated rete ridges were significantly more frequently observed in psoriasis. Follicular plugging, shoulder parakeratosis and prominent lymphocytic exocytosis were significantly more common in seborrheic dermatitis. Moreover, significantly higher mitotic figures were observed in psoriatic lesions than in seborrheic dermatitis. Immunohistochemistry did not show any difference between psoriasis and seborrheic dermatitis.
  
  
  CONCLUSIONS
  Histopathological features favoring psoriasis include mounds of parakeratosis with neutrophils, spongiform micropustules of Kogoj, clubbed and evenly elongated rete ridges, and increased mitotic figures (≥6/high-powered field). Features indicating seborrheic dermatitis are follicular plugging, shoulder parakeratosis and prominent lymphocytic exocytosis. Immunohistochemistry was not helpful in differentiating psoriasis from seborrheic dermatitis.
authors.affiliation: Department of Dermatology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Ji-Hye
authors.initials: JH
authors.lastname: Park
authors.affiliation: Department of Dermatology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Young Joon
authors.initials: YJ
authors.lastname: Park
authors.affiliation: Department of Dermatology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Sue Kyoung
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Department of Pathology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Ji Eun
authors.initials: JE
authors.lastname: Kwon
authors.affiliation: Department of Dermatology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Hee Young
authors.initials: HY
authors.lastname: Kang
authors.affiliation: Department of Dermatology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: Eun-So
authors.initials: ES
authors.lastname: Lee
authors.affiliation: Department of Dermatology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Jee Ho
authors.initials: JH
authors.lastname: Choi
authors.affiliation: Department of Dermatology, Ajou University School of Medicine, Suwon, Korea.
authors.forename: You Chan
authors.initials: YC
authors.lastname: Kim
keywords: Differential diagnosis; Psoriasis; Scalp; Seborrheic dermatitis