Electrolyte replacement in MG

Q: Which electrolyte replacement should be done with caution in ICU in patients with Myasthenia Gravis (MG)?



Answer: Magnesium

Magnesium acts at the neuromuscular junction by inhibiting the presynaptic release of acetylcholine and desensitizing the postsynaptic membrane. This can exacerbate the respiratory insufficiency in patients who are admitted to ICU with MG and may lead to the need for invasive ventilation. 

This becomes complicated in patients who require magnesium but may have an underlying disease of MG, like pre-eclampsia (see reference#2). In such cases, other agents should be used per symptoms, and expertise in such areas should be sought.

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References:

1. Paramveer Singh, Olakunle Idowu, Imrana Malik, Joseph L. Nates: Case-report: Acute Respiratory Failure Induced by Magnesium Replacement in a 62-Year-Old Woman with Myasthenia Gravis - Tex Heart Inst J 2015;42(5):495-7

2. Adam J. Lake, Antoun Al Khabbaz, and Renée Keeney Severe Preeclampsia in the Setting of Myasthenia Gravis Case Reports in Obstetrics and Gynecology / 2017 / Article ID 9204930 || https://doi.org/10.1155/2017/9204930