Flushing out the diagnosis.

A 30-year-old man presented with a 4-h history of severe headache, vomiting, diarrhoea and epigastric pain. 1 week previously, he had undergone a left hip arthroscopy in another hospital. He had no other medical history and his only medication was naproxen for post-operative pain. His blood pressure was 70mmHg systolic, pulse rate 130 bpm, respiratory rate 24 bpm and temperature was 38.38C. Physical examination was notable for a diffuse erythematous, blanching rash involving his face and trunk, conjunctival suffusion and mild abdominal tenderness. Laboratory studies were normal apart from a leucocytosis (18.1 10/l) and a creatinine of 149mmol/l. The provisional diagnosis was of toxic shock syndrome (TSS) secondary to peri-operative staphylococcal infection of the hip joint. He stabilized initially with fluid resuscitation and intravenous ceftriaxone, vancomycin and clindamycin. A contrast-enhanced computed tomography scan of his head and abdomen was normal. His medical condition deteriorated requiring endotracheal intubation and vasopressors with intravenous hydrocortisone for worsening vasodilatory shock. Orthopaedic surgery explored his left hip joint and it appeared clean. Synovial fluid gram stain was negative. He rapidly improved in the intensive care unit, was extubated, weaned from vasopressors and was subsequently discharged 1 week later. The rash resolved entirely during the admission. There was concern over the diagnosis of TSS as no staphylococcal or other micro-organisms were identified in blood or synovial fluid cultures and he did not fulfil the clinical criteria for diagnosis of TSS Although the rash did not recur, he returned some months later complaining of episodic facial flushing, diarrhoea and headache prompting further investigations. Urinary catecholamines, metanephrines and 5-indolacetamatic acid were normal as were thyroid function tests, synacthen test and calcitonin levels. Serum tryptase was elevated at 23.7 mg/l(normal: 2–14). This indicated increased mast cell burden or activation. A bone marrow biopsy confirmed a diagnosis of systemic mastocytosis (SM), demonstrating characteristic overpopulation of morphologically abnormal mast cells with the gain of function KIT D816V mutation (Figure 1).