Prurigo nodularis is an uncommon lesion that presents as extremely pruritic nodules with a wide anatomical distribution but particularly on extensor aspects of limbs.
Often lesions are multiple but solitary nodules can occasionally occur.
Lesions tend to be symmetrical and are associated with excoriations.
Females are more often affected than males.
Many authors consider this condition as part of the spectrum of lichen simplex.
Atypical mycobacteria may be a contributing factor in prurigo nodularis.
Microscopic features: Microscopic Image
Histopathology reveals psoriasiform hyperplasia or pseudo- epitheliomatous hyperplasia ;
Marked hyperkeratosis with hypergranulosis and focal parakeratosis ;
Occasional spongiosis and exocytosis of mononuclear cells;
Scale crust formation in association with changes of excoriation (fibrin deposition and cellular debris) ;
Prominent hyperplasia of hair follicles;
Mild fibosis of papillary and superficial dermis and telangiectasia ;
Mild to moderate perivascular mononuclear inflammatory cell infiltrate composed of lymphocytes , histiocytes and plasma cells ;
Nerve hyperplasia as reported in the past is not usually a feature.
Differential diagnosis: Diagnosis is not difficult if the biopsy is big enough. In small biopsies differential diagnosis include Keratoacanthoma and other causes of pseudo- epitheliomatous hyperplasia.
Note: Pseudoepitheliomatous (pseudocarcinomatous) hyperplasia : This is a benign pathological reaction pattern, histologically characterized by bulbous thickening of squamous epithelium (follicular infundibula and acrosyringium). There is abrupt transition beween lesion and adjacent epidermis. The cells have abundant often glassy cytoplasm .
Pseudoepitheliomatous hyperplasia is seen in the following conditions:
Chronic irritation ; skin trauma ; dermal inflammatory processes like chromomycosis ; aspergillosis ; pyoderma, Prurigo nodularis ; Granuloma fissuratum and in associatiation with chondrodermatitis nodularis helicis ; Spitz naevus , melanoma, overlying granular cell tumour and cutaneous T cell tumour .
Prurigo nodularis: a review.Australas J Dermatol. 2005 Nov;46(4):211-18; quiz 219-20.
Increased nerve growth factor- and tyrosine kinase A-like immunoreactivities in prurigo nodularis skin -- an exploration of the cause of neurohyperplasia.Arch Dermatol Res. 2002 Feb;293(12):614-9. Epub 2002 Feb 5.
Eosinophil cationic protein- and eosinophil-derived neurotoxin/eosinophil protein X-immunoreactive eosinophils in prurigo nodularis.Arch Dermatol Res. 2000 Aug;292(8):371-8.
Light and electron microscopic immunohistochemical observations of p75 nerve growth factor receptor-immunoreactive dermal nerves in prurigo nodularis.Arch Dermatol Res. 1999 Jan;291(1):14-21.
Helicobacter pylori and prurigo nodularis..Hepatogastroenterology. 1999 Jul-Aug;46(28):2269-72.
Histamine-containing mast cells and their relationship to NGFr-immunoreactive nerves in prurigo nodularis: a reappraisal.J Cutan Pathol. 1998 Apr;25(4):189-98.
Syringomatous changes of eccrine sweat ducts associated with prurigo nodularis.Am J Dermatopathol. 1998 Jun;20(3):296-301
Histopathological and bacteriological findings in prurigo nodularis.Acta Derm Venereol. 1997 Jan;77(1):49-51.
Mycobacteria in prurigo nodularis: the cause or a consequence?J Am Acad Dermatol. 1996 Feb;34(2 Pt 1):224-8.
Merkel cells and prurigo nodularis. J Am Acad Dermatol. 1994 Jul;31(1):86-8.
Mast cells, neutrophils, and eosinophils in prurigo nodularis. Arch Dermatol.1993 Jul;129(7):861-5.
Demonstration by S-100 protein staining of increased numbers of nerves in the papillary dermis of patients with prurigo nodularis.J Am Acad Dermatol. 1992 Jan;26(1):56-8.
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