Prurigo Nodularis
Christine J. Ko, MD
Key Facts
Etiology/Pathogenesis
Chronic rubbing/scratching induces discrete papules/nodules
Clinical Issues
Generally on extremities but sometimes on trunk or posterior scalp
Microscopic Pathology
Hyperkeratosis, focal parakeratosis, hypergranulosis
Acanthosis and sometimes pseudoepitheliomatous hyperplasia
Vertical streaking of collagen in papillary dermis
Minimal keratinocyte atypia
Top Differential Diagnoses
Squamous cell carcinoma (SCC)
Keratoacanthoma (KA)
Lichen simplex chronicus (LSC)
Deep fungal and atypical mycobacterial infection
 Low-power view of prurigo nodularis shows prominent hyperkeratosis  , parakeratosis, and hypergranulosis  overlying irregular acanthosis  with vertical streaking of collagen in the papillary dermis. |
 High magnification of prurigo nodularis shows hypergranulosis  . There is vertical streaking of collagen bundles present in the papillary dermis  , a finding seen in both prurigo nodularis and lichen simplex chronicus. |
TERMINOLOGY
Abbreviations
Prurigo nodularis (PN)
Definitions
Pruritic nodules
Generally on extensor surfaces of extremities
Secondary to chronic rubbing/scratching
ETIOLOGY/PATHOGENESIS
