How do you treat tetany in Myotonia Congenita?

Treatment of Tetany in Thomsen's Disease (Myotonia Congenita)

Intravenous magnesium sulfate is the first-line treatment for tetany in patients with Thomsen's disease (myotonia congenita), as it directly addresses the neuromuscular hyperexcitability that characterizes tetany. 1

Understanding Tetany in Myotonia Congenita

Tetany in myotonia congenita is a neurological manifestation characterized by:

• Neuromuscular hyperexcitability
• Involuntary muscle contractions
• Paresthesias (particularly circumoral and distal)
• Carpopedal spasm
• Potential for laryngospasm in severe cases

Unlike the myotonic symptoms typical of Thomsen's disease (muscle stiffness that improves with repeated use), tetany represents an acute complication that requires prompt intervention.

Diagnostic Approach

When evaluating tetany in a patient with myotonia congenita, assess for:

1. Electrolyte abnormalities:

   • Serum calcium (hypocalcemia is a common trigger)
   • Serum magnesium (hypomagnesemia often underlies tetany)
   • Serum potassium (hypokalaemia can contribute)
   • Acid-base status (alkalosis can precipitate tetany) 2

2. Clinical signs:

   • Chvostek sign (facial muscle spasm elicited by tapping facial nerve)
   • Trousseau sign (carpopedal spasm induced by occluding blood flow to arm)
   • Presence of paresthesias, muscle cramps, or laryngospasm 3

Treatment Algorithm

Acute Management

1. First-line treatment:

   • Intravenous magnesium sulfate for replacement therapy in acute tetany 1
   • Initial dose: 2g IV over 10-15 minutes for adults
   • Monitor for resolution of symptoms

2. If hypocalcemia is present:

   • IV calcium gluconate 10% solution (10ml over 10 minutes)
   • Follow with calcium infusion until symptoms resolve 4

3. For severe symptoms (laryngospasm, generalized seizures):

   • Ensure airway protection
   • Administer IV magnesium and calcium more urgently
   • Consider ICU monitoring if respiratory compromise occurs 3

Maintenance Therapy

1. Oral supplementation:

   • Oral magnesium supplements to maintain normal serum levels
   • Oral calcium supplements if hypocalcemia persists
   • Consider vitamin D supplementation to optimize calcium absorption 4

2. Medication adjustments:

   • Review and potentially modify medications that may exacerbate tetany (proton pump inhibitors, diuretics)
   • Avoid medications that worsen myotonia (beta-blockers, certain antidepressants) 2

Monitoring and Follow-up

• Regular monitoring of serum electrolytes (magnesium, calcium, potassium)
• Assessment of acid-base status if symptoms recur
• Evaluation for underlying causes of electrolyte disturbances

Special Considerations

• Avoid hyperventilation: Can induce respiratory alkalosis and worsen tetany
• Stress management: Stress can trigger both myotonia and tetany symptoms
• Hydration: Maintain adequate hydration to prevent electrolyte imbalances

Pitfalls to Avoid

1. Misdiagnosis: Don't confuse tetany with worsening myotonia - they require different management approaches
2. Overlooking hypomagnesemia: Even when calcium levels are corrected, persistent hypomagnesemia can maintain tetany 5
3. Inadequate monitoring: Tetany can progress to life-threatening complications like laryngospasm if not properly managed
4. Treating only the acute episode: Identifying and addressing the underlying cause of electrolyte disturbance is essential for preventing recurrence

By promptly recognizing and treating tetany in patients with myotonia congenita using IV magnesium sulfate as the cornerstone of therapy, clinicians can effectively manage this potentially serious complication and improve patient outcomes.