Avoid missing a rare condition by colouring your judgment purple

A 29 year old woman was admitted to the medical ward feeling generally unwell with a one week history of bilateral leg weakness, increased anxiety, and labile mood. She also described a five month history of blistering on the face, chest, and dorsum of her hands, without a confirmed diagnosis. She had previously seen her general practitioner and also attended the emergency department complaining of abdominal and back pain, sometimes associated with vomiting, but no diagnosis had been made and she had not been referred to dermatology. Her medical history included bipolar disease diagnosed five years ago, which was controlled with sodium valproate, and bulimia.

On examination, there were multiple angulated erosions on her face and upper chest (fig 1A). A single large irregularly shaped tense bulla was present on the dorsum of the right hand surrounded by a few smaller erosions on both hands. Scarring and milia were also noted at sites of previous blisters (fig 1B). Systemic examination was unremarkable. Blood testing showed a normal full blood count and liver and renal function. Sodium level was low at 130 mEq/L. (normal range 133-146), C reactive protein was <5, and an autoimmune screen (antinuclear antibodies, extractable nuclear antigens, double stranded DNA, C3, C4) was negative. A chest radiograph was normal and an electrocardiogram showed sinus tachycardia at 102 beats/min.