Case Quiz (August 2016)
A male infant presented with recurrent episodes of hyperkalaemia and acidosis since birth. He was born by normal vaginal delivery at term weighing 2.7 kg (9th centile) with a head circumference of 33 cm (9th centile). At 1 month of age, the boy was admitted to the local hospital with a week’s history of “funny spells”, where he had extensor posturing of his trunk and limbs and cried out. These lasted for 2–3 min at a time. There was no apparent relationship to feeding or passing bowel motions. On examination, the child was noted to be thriving, with a weight of 3.29 kg (2nd centile), a head circumference of 36 cm (9th centile) and a length of 52 cm (9th centile). Blood pressure was 78/52 mmHg. Clinical examination was unremarkable. He was not dehydrated on clinical assessment. The external genitalia appeared normal.Initial blood investigations showed serum potassium 7 mmol/l, sodium 142 mmol/l, chloride 112 mmol/l, bicarbonate 19 mmol/l, urea 2.1 mmol/ l and creatinine 0.29 mg/dl. The complete blood count showed normal haemoglobin, white blood cell and platelet values. Liver function tests were within normal limits. Calcium, phosphate, glucose and magnesium were within the normal range. Serum ammonia, lactate and creatinine kinase were normal. Capillary blood gas showed a mild metabolic acidosis with a base deficit of −5.2. A complete septic screen was negative. Cerebrospinal fluid (CSF) lactate, plasma and CSF amino acids; random cortisol; thyroid function tests; and 17- hydroxyprogesterone were all within the normal range. Serum aldosterone was entirely normal for age at 454 pmol/l (normal 300–1,500 pmol/l). Plasma renin activity was low at <0.2 nmol/l per hour (normal 1.1– 2.7 nmol/l per hour). Urinary potassium was 10 mmol/l, urine osmolality 151 mmol/l and plasma osmolality 290 mmol/l. Urinary screen for drugs and toxins was negative. An ultrasound scan of the renal tract demonstrated two normal kidneys. The child had a trial of sodium bicarbonate, fludrocortisone and calcium resonium at 2 months of age. However, these were not sufficient to correct the hyperkalaemia, which at this stage was associated with poor weight gain (3.7 kg, 0.4th centile). He was then commenced on low-potassium-containing milk. This corrected the hyperkalaemia. He was discharged home with serum potassium 3.8 mmol/l, sodium 139 mmol/l, chloride 100 mmol/l, urea 1.2 mmol/l and creatinine 18 μmol/l.
Case Answer (August 2016)
Pseudohypoaldosteronism type II [PHA type II] (Gordon’s syndrome or familial hypertension with hyperkalaemia) exhibits an autosomal dominant mode of transmission and is usually seen in late childhoodor adulthood. Persistent hyperkalemia in association with a normal GFR, hyperchloraemic metabolic acidosis and normal anion gap suggests aldosterone deficiency or aldosterone resistance in the distal nephron. Calculating the TTKG is a useful tool inthe assessment of renal handling of potassium with high values in the setting of hyperkalaemia suggesting hyperaldosteronism or PHA. mutations in the WNK kinases and characterised clinically by persistent hyperkalaemia, poor growth and hypertension. Treatment consists of a low salt diet and a thiazide diuretic, which reduces chloride intake and blocks NCC, respectively.
