31 years old female presented to casualty with acute abdominal pain and vomiting. The physical findings showed acutely unwell female with persistent regular tachycardia and a large goitre with a bruit. There were no demonstrable eye signs indicating Graves disease. Initial investigation showed profound high anion gap metabolic acidosis (PH-7.13,HCO3-5.1, CL-113.6 BE-22.1PCO2 2.69,PO2-12.5) and severe hyperthyroidism (FT4-44 picomol per litre,FT3-24.8 picomol per litre,TSH-<0.01 mu per litre) and presence of thyroid peroxidase antibodies suggesting autoimmune aetiology. Other investigations showed normal renal functions normal serum glucose, amylase, lactate and high normal basal cortisol levels and minimally elevated transaminases.Blood count showed polymorphonuclear leucocytosis with normal inflammatory markers.Her investigations also excluded paracetamol, salycylate poisoning and porphyria. Laparoscopy excluded acute abdominal pathology. Presumptive diagnosis of thyroid storm was made and treatment commenced.
Few hours after admission her clinical condition rapidly deteriorated causing hypotension and diminution of urine output and drop of GCS requiring intubation and ventilation. Initial treatment included beta blockers,antithyroid medications and intravenous steroids. Haemodiafiltration was used to manage subsequent deterioration of renal function. Over next few days she made a rapid clinical and biochemical improvement with normalisation of acid base status and improvement of thyroid functions. Further investigation into the cause of acidosis revealed evidence of medium-chain acyl-coenzyme A dehydrogenase(MCAD) deficiency.
MCAD deficiency is a uncommon condition that prevents beta oxidation of fatty acids of medium chain length particularly during periods of fasting. Acidosis in MCAD deficiency is probably due to accumulation of decarboxylic acids from omega oxidation of medium chain fatty acids through an alternative pathway. Hyper metabolic state in thyroid storm is probably responsible for the unmasking of this uncommon disorder of fatty acid metabolism.