Pyoderma gangrenosum — a frequently misdiagnosed skin condition

Pyoderma gangrenosum (PG) is a painful destructive skin condition, which often presents as progressive deep ulcerations or superficial bullous erosions. It frequently causes significant morbidity because of delays in diagnosis and consequent delays in instituting effective treatments. A recent case report from the United Kingdom highlights a sequence of events that is repeated with often devastating consequences.1 The report describes a woman who re-presented to the hospital 2 weeks after a laparoscopic abdominal-approach perineal hernia repair with severe abdominal pain and oozing from a wound site, and was treated for cellulitis. Antibiotics were continued despite progression of the lesion and negative cultures. Only when the situation progressed to “an ulcerating, macerated, hyperalgesic lesion involving the entire anterior abdominal wall”, was a dermatologist contacted, the correct diagnosis made, and the appropriate treatment instituted.1

PG is rare, with an estimated incidence in the order of three cases per 1 million population per year.2 The aetiology remains uncertain, but it is best thought of as an autoimmune process characterised by a sterile neutrophilic infiltrate. It is presumed that cytokine release attracts neutrophils. The fact that 25% of cases of PG show pathergy (where the condition appears at the site of skin trauma), as in this case, suggests a malfunction of the inflammatory phase of the normal wound healing process.

Severe pain often out of proportion to the physical findings is a common feature of PG.2 The clinical presentation may be variable, with ulcerative, pustular, bullous or vegetative forms being described.2 One distinctive and at times difficult to manage variant is peristomal PG, again thought to result from the pathergic effect of skin trauma or inflammation in this area.

The diagnosis of PG is based mainly on the clinical setting, the patient’s history and the physical features of the lesion in question (Box). Skin biopsy can be useful even though there is no diagnostic histological feature to confirm the diagnosis.2 The histopathological examination can help exclude other diagnoses, such as malignancy or infection, while at the same time showing features that an experienced histopathologist can identify as suggestive of a diagnosis of PG.

About half of all cases of PG occur in isolation, with no identifiable underlying or associated medical conditions; the remainder occur in patients who have various systemic inflammatory conditions, such as rheumatoid arthritis, inflammatory bowel disease, and other autoimmune conditions (Box). PG has also been reported in association with various malignancies, particularly haematological, including monoclonal gammopathies.3

The management involves pain relief, confirmation of the diagnosis, wound care and topical therapies, and systemic therapies. Severe cases require inpatient treatment to closely monitor pain relief and response to therapy. The initial treatment is usually with prednisolone in medium to high doses (0.5–1.0 mg/kg/day) or, rarely and in severe resistant cases, with intravenous pulsed therapy.2-4 Since there are cases of PG that do not respond to systemic corticosteroids alone, other agents may be used, either in isolation or in combination with steroids, and include mycophenolate mofetil, azathioprine, methotrexate, tacrolimus, cyclosporin and infliximab.2-4

Also, as PG lesions can take months to heal fully, using a steroid-sparing agent, such as dapsone or minocycline, is recommended to minimise the side effects of long-term steroid therapy.

Establishing the correct diagnosis is vital, as incorrectly labelling patients with PG can expose them unnecessarily to the toxicities of these treatments.5 Conditions mistakenly diagnosed and treated as PG include infection, vascular inflammation (vasculitis), vascular occlusion or venous disease, malignant ulcerations and exogenous tissue injury, including artefacts.5

What lessons are there to be learnt from this case report? The patient presented with a wound site ulceration to a surgical unit. Infection was assumed to be the cause. The potential for an alternative diagnosis in this clinical setting with potentially serious consequences was not recognised at the initial stages, and the appropriate specialist, the dermatologist, was not consulted until major ulceration developed and anti-infection treatments failed.

When confronted with unexpected changes in the skin, such as the sudden onset of very painful rapidly progressive ulceration for no readily apparent reason, particularly at the site of previous skin trauma, medical practitioners should take a step back and consider the clinical context in which these changes are occurring. Are there reasons other than infection that could account for this development? If the patient is afebrile, if the microbiologic cultures are negative, if antibiotic therapy is not rapidly effective — don’t delay! Call the dermatologist!