Introduction: Hypokalaemia is a common biochemical abnormality seen in inpatients; it is usually mild and iatrogenic. We report a rare case of muscle paralysis due to severe unprovoked hypokalaemia, presenting on acute medical take.
Case: The patient presented with a two week history of epigastric pain, nausea, vomiting, muscle spasms and dizziness. Past medical history included asthma, vitiligo, pernicious anaemia as well as long standing history of unexplained collapses. Possibility of Addisons had been excluded in the past following a short stint of steroid therapy.
Initial Investigations: Serum potassium 2.0 (3.55.3 mmol/l), bicarbonate 18 (2229 mmol/l), Chloride 114 (95108 mmol/l), ALP 366 (38126 U/l), ALT 135 (050 U/l), random cortisol 273 nmol/l. She was commenced on steroids and intravenous Potassium in the Emergency department. However, a day later she developed breathlessness with progressive paralysis of all limbs (−4/5). Consequently she required closed monitoring with repeated potassium infusion via central access. Restoring potassium within normal range resulted in complete neurological recovery. Once stable she was switched to Spironolactone (while aldosterone levels pending) and oral potassium replacement to good effect. Steroids were stopped given an optimal response to Synacthen (peak of 533 nmol/l).
Further investigation: Hyperchloraemic metabolic acidosis with a pH of 7.27, potassium remained low at 1.9 mmol/l, Urinary pH of 7, 24 h urinary potassium excretion of 131(3590 mmol), anti-adrenal antibodies were negative, aldosterone:renin ratio was 43 (<64), liver ultrasound was unremarkable. The sustained metabolic acidosis, hypokalaemia and urinary pH>5.5 were in-keeping with distal renal tubular acidosis (dRTA).
Conclusion: dRTA is a disorder of renal acidification characterized by inability to acidify urine to pH <5.5 despite the presence of systemic metabolic acidosis and hypokalaemia. Hypokalaemia leads to acute onset paralysis and may be a presenting symptom of dRTA. This case report highlights the importance of considering dRTA in the differential diagnosis of severe hypokalaemia.