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Taking it on the shin: Part one

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By Warren R. Heymann, MD, FAAD
May 31, 2023
Vol. 5, No. 22

Dr. Warren Heymann photo
I am intentionally skeptical of medical literature that purports “new” entities. Are they novel and distinct or just minor variations of long-recognized dermatoses? This two-part commentary will focus on two disorders that involve the pretibial region — pretibial pruritic papular dermatitis (PPPD) and obesity-associated lymphedematous mucinosis (OALM). I have come to believe in both. You have likely encountered these conditions but may not have realized it. 

Scenario 1: A 60-year-old healthy woman complains of constant pruritus of her shins. Your examination demonstrates somewhat cobblestone pink-red papules within a plaque. Your initial impressions are lichen amyloidosis, lichen simplex chronicus, prurigo nodularis, lichen planus, or contact dermatitis (irritant or allergic). Your biopsy fails to show amyloid deposition, prominent epidermal hyperplasia, vertical streaking of papillary dermal collagen, a lichenoid infiltrate, or significant spongiosis, ruling out these disorders, respectively. Patch testing was negative. Fortunately, she responds to potent topical steroids, although the disorder requires intermittent therapy for periodic recurrences. PPPD is the probable diagnosis.

Annessi et al initially reported PPPD in 2006: “We describe the clinico-pathologic features of 44 patients with a peculiar pretibial pruritic papular dermatitis (PPPD). Clinically, PPPD consists of discrete, roundish, extremely pruritic papules with a smooth surface caused by the delicate and persistent rubbing of pretibial skin. Histologically, PPPD showed minimal compact orthokeratosis, flattening of the rete ridges, a superficial and mid-dermal perivascular and interstitial infiltrate of lymphocytes, histiocytes, eosinophils and multinucleated fibroblasts, and thickened collagen bundles in haphazard array in the superficial dermis. The clinical picture of PPPD closely resembled that of lichen simplex chronicus/circumscribed neurodermatitis or lichen amyloidosus. Histologically, the absence of uneven psoriasiform epidermal hyperplasia, marked compact orthokeratosis, hypergranulosis, and coarse bundles of collagen arranged in vertical streaks in the papillary dermis distinguished PPPD from lichen simplex chronicus, whereas the lack of amyloid deposits in the dermal papillae differentiated PPPD from lichen amyloidosus. We suggest that PPPD is an unusual morphologic expression of gentle and chronic rubbing of pretibial skin with distinctive histopathologic features.” In their conclusion, the authors stated: “We feel that PPPD could be the result of a combination of several factors, including genetic influences, cutaneous xerosis, contacts with irritants, the modality of rubbing, the skin area, and emotional distress.” (1)

The case of PPPD reported by Noakes and Mellick is of interest. A 44-year-old woman with a history of atopy presented with lesions that I would have diagnosed clinically as lichen amyloidosis; her biopsy was consistent with PPPD, although eosinophils were readily apparent. (2) I could not find mention of patch testing in this patient, but under these circumstances, I would be reluctant to diagnose PPPD without that assessment.

lichen amyloidosis
Image of lichen amyloidosis from DermNetNZ.
The etiology of PPPD remains obscure. Although a likely reaction to gentle rubbing of the pretibial region, it could be a response to different underlying systemic diseases or other dermatoses. (3) Flores et al performed a retrospective observational study of 40 archived pathological specimens (hematoxylin/eosin, CD3, CD20, and CD30 immunohistochemistry) from 38 PPPD patients; clinical images were available in 22 patients. The authors found a broader histological and clinical spectrum of PPPD than previously described; epidermal changes are common in PPPD, as are atypical lymphocytes and focal CD30 positivity. (4)

In a dermatoscopic study of 7 patients with PPPD, the following features were observed: dotted or globular vessels over a pinkish-whitish background (7/7, 100%); peripheral, whitish collarette scaling with a petaloid appearance (5/7 cases; 71%); and hemorrhagic crusts and sparse whitish scales (4/7, 57%). (5)

Therapy has focused on the use of topical steroids (with or without occlusion) although I suspect that calcineurin inhibitors, phosphodiesterase inhibitors, aryl hydrocarbon receptor agonists, and JAK inhibitors would all be beneficial. The real value is in placing a name on a disorder —patients are reassured their malady is defined, even though we do not understand it. Hopefully, that will change as more cases are described and scrutinized.

Point to Remember: Pretibial pruritic papular dermatitis is a dermatosis that is a likely reaction pattern to a variety of stimuli. The diagnosis may be rendered after considering other clinically similar entities such as lichen amyloidosis, lichen simplex chronicus, and allergic contact dermatitis. 

Our expert’s viewpoint

Kiran Motaparthi, MD, FAAD
Associate Professor
Residency Program Director
Director of Dermatopathology
Department of Dermatology
University of Florida College of Medicine

Although the two main studies of PPPD were published in dermatopathology journals, it is unlikely that clinicians would ever receive a definitive report of this diagnosis from their dermatopathologists. (1,4) As Dr. Heymann notes, the consistent histopathologic features of PPPD include dermal fibrosis, stellate and multinucleate fibroblasts, and a perivascular and interstitial lymphohistiocytic infiltrate. (1,4) Unfortunately, none of these dermal changes are specific, and all of them can be observed in a chronic eczematous disorder, which is most likely what PPPD truly represents. The expanded spectrum of findings — which includes epidermal changes (irregular psoriasiform hyperplasia, compact orthohyperkeratosis, erosion) analogous to lichen simplex chronicus, eosinophils, and CD30-positive atypical lymphocytes — makes histopathologic diagnosis even more challenging. The accurate diagnosis of PPPD relies on correlation by astute clinicians who recognize the consistent features of this rare disorder in a microscopic description, even if they initially considered more common dermatoses at the time of biopsy, such as lichen simplex chronicus or lichen amyloidosis.

  1. Annessi G, Petresca M, Petresca A. Pretibial pruritic papular dermatitis: A distinctive cutaneous manifestation in response to chronic rubbing. Am J Dermatopathol. 2006 Apr;28(2):117-21. doi: 10.1097/01.dad.0000200017.37082.e4. PMID: 16625072.

  2. Noakes R, Mellick N. Case of pretibial pruritic papular dermatitis. Letters to the editor. Australas J Dermatol. 2010 Aug;51(3):215-6. doi: 10.1111/j.1440-0960.2010.00667.x. PMID: 20695866.

  3. Kecelj B, Kecelj Leskovec N, Žgavec B. A case report and differential diagnosis of pruritic pretibial skin lesions. Acta Dermatovenerol Alp PannonicaAdriat. 2020 Sep;29(3):157-159. PMID: 32975304.

  4. Flores S, Wada DA, Florell SR, Bowen AR. Pretibial Pruritic Papular Dermatitis: A Comprehensive Clinical and Pathologic Review of Cases at a Single Institution. Am J Dermatopathol. 2020 Jan;42(1):16-19. doi: 10.1097/DAD.0000000000001460. PMID: 31188140.

  5. Errichetti E, Stinco G. Dermoscopy for improving the diagnosis of pretibial pruritic papular dermatitis. Australas J Dermatol. 2018 Feb;59(1):e74-e75. doi: 10.1111/ajd.12610. Epub 2017 Jun 21. PMID: 28636138.

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