CASE REPORT A woman with generalised weakness, hypokalaemia, and metabolic acidosis H U Rehman clinical associate professor Department of Medicine, Regina Qu’Appelle Health Region, Regina General Hospital, Regina, SK, Canada S4P 0W5 A 31 year old woman presented with generalised weakness and muscle pain a week after having a flu-like illness, which had resolved completely. She had no diarrhoea, vomiting, urinary symptoms, joint pains, rashes, dry eyes, or dry mouth. Her medical history was unremarkable. Physical examination showed that she was well hydrated. Blood pressure was 102/55 mm Hg, pulse rate 88 beats/min. Muscle strength was 4/5 and 0/5 in the flexor muscle groups and 1/5 and 4/5 in the extensor muscle groups of the upper limbs and lower limbs, respectively. Deep tendon reflexes were brisk in the upper and lower limbs. No sensory deficit was found and the Babinski reflex test was negative. The rest of the physical examination was unremarkable. Initial blood results were sodium 141 mmol/L (normal range 135-145), potassium 1.7 mmol/L (3.5-5.0), chloride 118 mmol/L (98-110), carbon dioxide 14 mmol/L (21-30), anion gap 11 mmol/L (10-20), urea 5.4 mmol/L (3.0-7.1), creatinine 69 µmol/L (60-130), creatine kinase 320 U/L (30-135). Urine results were pH 7.00 (5.0-8.0), sodium 47 mmol/L, potassium 13.2 mmol/L, chloride 52 mmol/L, calcium 1.50 mmol/L, and creatinine 3.9 mmol/L. Arterial blood gases on room air showed pH 7.31 (7.35-7.45), partial pressure of carbon dioxide 26 mm Hg (33-45), partial pressure of oxygen 111 mm Hg (75-100), bicarbonate 15 mmol/L (22-26), and base excess −12.1 mmol/L (−2.5 to 2.5). Erythrocyte sedimentation rate was 106 mm in the first hour (0-20). Complete blood count, thyroid function tests, and liver panel were normal. She had a polyclonal increase in gammaglobulins 24.5g (6.0-18.0), IgG of 27.90 g (5.52-17.24), but normal IgA and IgM. Antinuclear antibodies were positive at 1:320, with a finely speckled staining pattern. Anti-smooth muscle antibodies were positive to a titre of 1:20. Anti-double stranded DNA antibodies were negative. She was positive for anti-Ro/SSA antibodies but negative for anti-La/SSB antibodies. Renal ultrasound showed a stippled echogenic pattern of the renal pyramids related to nephrocalcinosis and small stones in the lower pole of the right kidney. Parathyroid hormone was 1.92 ng/L (1.3-6.8); 25-hydroxyvitamin D 3 59 nmol/L (25-250), rheumatoid factor 72 IU/mL (0-15), and caeruloplasmin 255 mg/L (200-600). Anti-cyclic citrullinated peptide antibodies were negative. Questions 1 What is the cause of hypokalaemia in this patient? 2 What is the underlying cause of the metabolic abnormality? 3 How would you treat this patient? Answers 1 What is the cause of hypokalaemia in this patient? Short answer Distal renal tubular acidosis. Long answer Renal tubular acidosis comprises a group of disorders that result from tubular damage without glomerular damage. Primary and acquired forms have been described. There are three major types: type 1 or distal renal tubular acidosis, where the basic defect is impaired excretion of hydrogen ions; type 2 or proximal renal tubular acidosis, where the basic defect is a failure in bicarbonate reabsorption; and type 4 renal tubular acidosis, which is caused by apparent or real aldosterone deficiency or resistance and is most commonly associated with diabetes or interstitial nephritis. Hyperchloraemic metabolic acidosis with a normal anion gap, with or without associated defects in potassium homeostasis, and a urine pH greater than 5.5 in the presence of acidaemia are the hallmark features of renal tubular acidosis. Kidneys respond to acidosis by increasing ammonium excretion in the urine. Failure of the kidney to increase ammonium output in the setting of acidosis indicates that a defect in renal acidification may be primarily responsible for the acidosis. 1 Because renal ammonium excretion is not measured directly in Correspondence to: H U Rehman habib31@sasktel.net For personal use only: See rights and reprints http://www.bmj.com/permissions Subscribe: http://www.bmj.com/subscribe BMJ 2012;344:e2545 doi: 10.1136/bmj.e2545 (Published 12 April 2012) Page 1 of 2 Endgames ENDGAMES