Pictorial case study: A painful ulcer

A supposed insect bite became a deep ulcer, explains Dr Jean Watkins.

A diagnosis of pyoderma gangrenosum was made (Photograph: Dr P Marazzi/SPL)
A diagnosis of pyoderma gangrenosum was made (Photograph: Dr P Marazzi/SPL)

The presentation
This 65-year-old woman noticed a small pimple on her shin. She had no recollection of any injury, so thought it might have been an insect bite. She did not take it too seriously until it broke down to form a painful, deep, weeping ulcer that rapidly increased in size. The edges of the crater-like ulcer appeared to overhang the ulcer bed. The history and findings were taken into account, with the knowledge that she was also known to have quite severe rheumatoid arthritis.

The management
A diagnosis of pyoderma gangrenosum was made. Secondary infection was excluded and the patient was referred urgently to a rheumatologist. She was started on minocycline, an oral steroid and ciclosporin. A nurse supervised wound care using foam, laminate alginate or wet compress dressings. As there was some oedema of the legs and evidence of varicose veins, but adequate circulation to the limbs, compression bandages were applied. The ulcer should heal but the process would be long and would leave a scar. There is a risk of further flare-up.  

Case discussion
Pyoderma gangrenosum is thought to be an autoimmune disorder and is a rare cause of ulceration of the skin. About 50% of cases are associated with an underlying systemic disease, such as ulcerative colitis or Crohn’s disease, rheumatoid arthritis, chronic active hepatitis or myeloid blood dyscrasias.

Pyoderma gangrenosum is more common over the age of 50. Lesions commonly occur on the legs but may appear anywhere on the body. Lesions may take the form of a small papule that rapidly breaks down to form a deep ulcer with overhanging edges; this may be accompanied by fever.

Sometimes, less aggressive lesions occur with more superficial ulceration. In cases of pustular pyoderma gangrenosum, there are multiple sterile pustules with a surrounding erythematous halo.

Swabs should be cultured to exclude secondary infection. Skin biopsy will not positively confirm the diagnosis but may be required to exclude other possible causes. FBC, ESR, CRP, LFTs, urinalysis and auto-antibodies may help to idenitfy an underlying cause.

Potent topical steroids or intralesional steroids may help small ulcers but more severe problems may require oral steroids and immunosuppressants.

Differential diagnoses

  • Arterial or venous ulcers
  • Vasculitis 
  • Infections, including herpes, TB or parasitic infections  
  • Malignancy
  • Injury and dermatitis artefacta

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