Wednesday, July 27, 2016

Consult Rounds: Hyponatremia and Rhabdomyolysis

A lesser known complication of hyponatremia or its correction is rhabdomyolysis. While recognized causes of rhabdomyolysis (Rb) include injury, seizures, drugs such as statins, hypokalemia and hypophosphatemia are known in the literature, less is known re association of hyponatremia leading to Rb.  

It was first described in 1979. In that patient, the low Na was from psychogenic polydipsia.
Multiple case reports following them( listed below) have been described in the literature. Most recently, this has been described in marathon runners that get both hyponatremic and Rb. In that study, the hyponatremic runners with the lowest post race Na demonstrated the highest CPK values at subsequent checkpoints. This is interesting.

What could be the mechanism?  What does the literature say?
1. Change in osmotic pressures results in failure of regulation of cell volume and cell lysis( so this could occur during hyponatremia or treatment of hyponatremia).
If the Na is corrected too rapidly, the cell has no time to compensate for the osmotic shifts and perhaps leads to Rb.
2. Na/Ca pump in muscle cells might be effected. As extracellular Na drops, Ca leaves the muscle cell and ensuing activation of cellular proteases leading to cell lysis.
3. Seizures leading to the rise in CPK

Situations where this has been described in the literature:
Most commonly: Psychogenic polydipsia
Others: use of thiazides, PPIs, Bactrim, marathon runners, adrenal insufficiency

Hmmm... Should we be checking CPKs in our severe hyponatremia cases? Should we be concerned about Rb in rapid correction ( more than CPM) as Rb is likely more commonly seen then CPM?

Here are some interesting references

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