Spontaneous expanding painful ulcer

N is a young girl with a painful spontaneous ulcer on her leg which enlarged quickly to 2.5cm in diameter over 3 weeks.

Ulcers can develop for many reasons - external injury and pressure (obviously), failure to sense pain (hence suffering repeated injury - usually in diabetics), blood vessel disease (eg varicose veins, blood vessel inflammation and/or obstruction) etc. The spontaneously-occurring ulcer you see here, however, is different from these. It expands very quickly, has a boggy edge and is painful. It is important to see a dermatologist ASAP to evaluate the cause as it looks like either a blood vessel inflammatory disease (which can be either on its own or involve internal organs too), or an uncommon 'skin-eating' disease called pyoderma gangrenosum (which also can be either on its own or related to an internal disease). Concomitant infection with bacteria should also be excluded and treated.