Gitelman syndrome

Background

• Gitelman syndrome is an autosomal recessive salt-losing tubulopathy caused by loss-of-function mutations in the thiazide-sensitive sodium-chloride cotransporter (NCC) in the distal convoluted tubule
• It is the most common inherited renal tubulopathy (~1 in 40,000) and presents with hypokalemic metabolic alkalosis, hypomagnesemia, and hypocalciuria — biochemically identical to chronic thiazide diuretic use
• Usually diagnosed in adolescence or adulthood, it is generally benign but can cause life-threatening hypokalemia, cardiac arrhythmias, tetany, paralysis, and rhabdomyolysis
• The EM physician encounters Gitelman syndrome as unexplained refractory hypokalemia in a young normotensive patient, tetany or muscle cramps, or cardiac arrhythmia from combined hypokalemia and hypomagnesemia
• Prevalence ~1 in 40,000 (heterozygote carrier frequency ~1% in Caucasians); higher in Asian populations
• Much more common than Bartter syndrome (~1 in 1,000,000)
• Usually presents after age 6; most diagnosed in adolescence or adulthood — many patients are asymptomatic for years
• Mimics chronic thiazide (HCTZ) use — the NCC cotransporter is the same target as thiazide diuretics
• Sudden cardiac death has been reported from severe hypokalemia/hypomagnesemia

Clinical Features

• Many patients are asymptomatic — discovered incidentally on routine labs showing hypokalemia
• Muscle cramps, weakness, fatigue — the most common complaints
• Tetany, carpopedal spasm — from hypomagnesemia; especially during illness or with vomiting/diarrhea
• Facial paresthesias — characteristic
• Salt craving (sometimes intense; also craving sour foods)
• Thirst, nocturia, polyuria (milder than Bartter)
• Constipation
• Low or normal blood pressure — despite elevated renin/aldosterone
• Chondrocalcinosis — calcium pyrophosphate crystal deposition in joints (from chronic hypomagnesemia); may present with acute pseudogout-like joint pain and swelling
• Prolonged QT interval — present in ~50%; risk of ventricular arrhythmias
• Severe presentations (uncommon): hypokalemic paralysis (especially in Asian populations), rhabdomyolysis, seizures, ventricular arrhythmia/cardiac arrest

Differential Diagnosis

• Bartter syndrome: the key differential — more severe, earlier onset, hypercalciuria (vs hypocalciuria in Gitelman), mimics loop diuretic (vs thiazide); see comparison table on Bartter syndrome page
• Surreptitious vomiting / bulimia: urine chloride <25 mEq/L (Gitelman: urine Cl >35 mEq/L)
• Thiazide diuretic use/abuse: identical lab picture — screen urine for diuretics
• Laxative abuse: low urine potassium (renal potassium wasting distinguishes Gitelman)
• Primary hyperaldosteronism: hypertension present (Gitelman is normotensive/hypotensive)
• Renal tubular acidosis: metabolic acidosis (not alkalosis)
• Hypomagnesemia from other causes: PPI use, alcoholism, aminoglycosides, cisplatin — check medication history
• Pseudogout (if presenting with chondrocalcinosis): check electrolytes in any young patient with calcium pyrophosphate arthropathy — may unmask Gitelman

Evaluation

Workup

• BMP: hypokalemia (often 2.5-3.0 mEq/L), hypochloremia, elevated bicarbonate (metabolic alkalosis)
• Magnesium: low (<1.6 mg/dL) in most patients — always check magnesium when you find hypokalemia
• Urine electrolytes:
  • Urine chloride >35 mEq/L — confirms renal salt wasting (excludes vomiting)
  • Urine potassium elevated (inappropriate renal K wasting)
  • Urine calcium:creatinine ratio LOW (hypocalciuria) — the key distinction from Bartter (which has hypercalciuria)
• ECG: prolonged QT, flattened T waves, U waves, ST depression; assess for arrhythmia
• Urine drug screen for diuretics — must exclude thiazide abuse before diagnosing Gitelman

Diagnosis

• Hypokalemic hypochloremic metabolic alkalosis + hypomagnesemia + hypocalciuria + normal/low BP + urine Cl >35 = Gitelman pattern
• Exclude vomiting (urine Cl <25), diuretic abuse (urine drug screen), and medications causing hypomagnesemia
• Genetic testing (SLC12A3 mutations) is confirmatory but not an ED test
• Clinical and biochemical diagnosis is sufficient to initiate treatment

Management

• Correct hypokalemia:
  • IV KCl for severe hypokalemia (<2.5 mEq/L), ECG changes, or arrhythmias
  • Oral KCl for mild-moderate cases
  • Correct hypomagnesemia FIRST — magnesium deficiency causes refractory hypokalemia that will not correct until magnesium is repleted
• Correct hypomagnesemia:
  • IV magnesium sulfate (2 g over 15-30 min, then infusion) for severe hypomagnesemia, tetany, or arrhythmias
  • Oral magnesium supplementation for chronic management (magnesium oxide, magnesium citrate)
  • GI side effects (diarrhea) limit oral magnesium dosing — a major compliance issue
• Cardiac monitoring: continuous telemetry if K <3.0 mEq/L, prolonged QT, or any arrhythmia
• Continue home medications: potassium-sparing diuretics (amiloride, spironolactone), oral potassium and magnesium supplements — do NOT discontinue
• Do NOT use thiazide diuretics — this worsens the underlying defect
• NSAIDs (indomethacin): sometimes used chronically as adjunctive therapy (reduces prostaglandin-mediated salt wasting) — continue if prescribed
• Treat precipitating illness: any condition causing vomiting, diarrhea, or fever can precipitate electrolyte crisis in Gitelman patients

Disposition

• Admit:
  • Severe hypokalemia (<2.5 mEq/L) or symptomatic hypokalemia (arrhythmia, paralysis, rhabdomyolysis)
  • Tetany or seizures
  • QT prolongation with arrhythmia
  • Unable to tolerate oral supplements
• Discharge with close follow-up:
  • Mild-moderate hypokalemia correctable with oral supplements
  • No cardiac symptoms or ECG abnormalities
  • Tolerating PO
  • Nephrology follow-up within 1-2 weeks
• New diagnosis suspected (unexplained hypokalemic alkalosis + hypomagnesemia + hypocalciuria in a normotensive patient): arrange nephrology referral for confirmation and long-term management
• Counsel patients: liberal salt intake; high-potassium foods; take magnesium and potassium supplements reliably; seek care promptly during illness (vomiting/diarrhea can precipitate dangerous electrolyte drops); report palpitations, weakness, or muscle spasms immediately

See Also

• Bartter syndrome
• Hypokalemia
• Hypomagnesemia
• Metabolic alkalosis
• Pseudogout

External Links

• StatPearls — Gitelman Syndrome
• Kidney Int — KDIGO Controversies Conference: Gitelman syndrome (2017)
• Orphanet J Rare Dis — Gitelman syndrome (2008)