Erosive Pustular Dermatosis
Author: Amrit Sanghera
Editors: Daniel Keith, Kalina Bridgewater
Introduction
Erosive Pustular Dermatosis (EPD) is a rare, chronic inflammatory condition that is characterised by painful erosions, crusts and sterile pustules. These develop on areas of the skin that are fragile or damaged. It may lead to scarring alopecia if it occurs on the scalp, which is hair loss where the hair roots are destroyed and cannot grow back.
Typically, there is a history of mechanical or chemical trauma to the scalp before this condition develops.
On pathology, EPD is characterised by atrophy of the epidermis layer of the skin and inflammation that consists of lymphocytes, neutrophils and occasionally, foreign giant body cells.
Clinical Presentation
Distribution:
The area most commonly affected is the scalp but it can also involve the lower legs over areas with thin or atrophic skin.
The vertex of the scalp tends to be most commonly affected followed by the frontal, parietal and temporal regions.
Clinical Features:
Red, inflamed, eroded patches
Sterile pustules (i.e. not caused by infection) which may be small and quickly rupture
The sterile green pus produced may form into a crust that hardens quickly and is large in size
Thick yellow-brown crusts that overly erosions Tender or painful in nature, occasionally itchy
Slow healing of lesions, which often leave behind a scar or atrophy of the skin or hair loss over time.
The image to the left below shows an example of a patient with EPD on his scalp. There is visible green-tinged crust, typically this can be can be soft and squidgy and leak out liquefied green pus from the side when squeezed.
Crust Removal
Top tip: It is an essential step to remove the crust with any lesion so that you can identify what lies underneath. The photographs above show the same patient before and after crust removal, which you can see look quite different.
1. Crusts are gently softened with use of either: white soft paraffin, emollient ointments or saline/water soaks. A thick layer is applied, lesion is covered with a non-adherent dressing and left on for 30-60minutes.
2. Gentle removal with gauze or cotton wool. Crusts should lift off easily.
3. Topical corticosteroids can then be applied and absorbed to treat the area by reducing inflammation.
Dermatoscopic Features:
Dermoscopy is not essential for diagnosis of EPD. However dermoscopy is becoming more common in primary care. When examined with a dermoscope, the region of the scalp shows absence of follicular ostia (tiny openings on the skin surface where hair follicles emerge) with marked atrophy of the skin, which allowed the vessels of the dermis to be visualised. There may also be visible patchy brown-grey hyperpigmentation of the skin.
Differentials:
The main differential is Squamous Cell Carcinoma. Cases of EPD are often referred to urgent skin cancer clinics under 2 week wait pathway in the UK as they fit the NICE criteria. More detail about Squamous Cell Carcinoma can be found here:
https://www.dermoscopea.com/squamous-cell-carcinoma
Features such as leaking yellow green pus on squeezing the crust and a lack of a painful nodule underneath the crust favour EPD, however if there is any doubt, then the patient must be referred under the suspected cancer pathway for timely specialist assessment.
If any of these features are present, a 2 week wait urgent suspected cancer referral is required:
Rapid growth
Bleeding
Pain or tenderness on palpation
Palpable lump
Take Home Message: EPD is a diagnosis of exclusion and if SCC is a differential, this warrants a 2 week wait urgent skin cancer clinic referral.