Rhabdomyolysis

 

Written by: Zachary Ravnitzky DO; Edited by: Timothy Khowong, MD, MSEd

 

What is Rhabdomyolysis?

Rhabdomyolysis is a breakdown of skeletal muscle, causing the breakdown products to be released into the blood and causing potential end organ failure.

Causes of Rhabdomyolsis

There are many causes of rhabdomyolysis, so I’ll break them down into a few major categories:

  1. Trauma: consider this for any trauma patient. Anything from MVA’s, falls, crush injuries, sports injuries, etc. 

  2. Post-operative: You can almost group this in with trauma. Surgery is traumatic and causes muscle injury. 

  3. Prolonged exercise: You should think of rhabdomyolysis if your patient just finished running the NYC marathon (but even short spurts of intense exercise or patients new to exercising can cause rhabdomyolysis. 

  4. Drugs: The classes of drugs to look out for are statins, SSRI’s, antipsychotics, succinylcholine (MH), Alcohol, Daptomycin.

  5. Infections: Flu, EBV, CMV, Hepatitis, strep, staph, etc. Sepsis can absolutely cause muscle injury. 

  6. Metabolic: Thyrotoxicosis, electrolyte derangements

  7. Autoimmune: SLE, polymyositis, autoimmune myocarditis

  8. Environmental: snake venoms, lead/mercury poisoning

  9. Others: seizures, dehydration, and burns. (These are actually some of the most common causes of rhabdomyolysis. )

Diagnosis

Labwork: It is common for doctors to classify the severity of rhabdomyolysis based on the Creatine Kinase (CK) levels as seen below. Although not perfect (which I will discuss soon) it is a nice framework to guide treatment and disposition. The numbers to pay attention to are 5,000 (indicating a true rhabdomyolysis) and 15,000 (indicating a severe case of rhabdomyolysis.)

But when is ordering a CK useful? Look at the graph below which shows serum myoglobin vs CK over time after any inciting event of rhabdomyolysis.

For example: A patient comes in at 12pm after just completing the NYC marathon. The patient complains of widespread pain, weakness, and has dark red urine x1 hour. We order a CK and it is only 957. 

At this point you are highly suspicious for rhabdomyolysis, but your CK is not congruent with a slam dunk diagnosis. 

This confusion can be alleviated when you look at the half lives of Myoglobin and CK. Myoglobin half-life is only 1-6 hours, so it will be quickly eliminated in the urine (making the patient have dark red urine.) CK levels, however, will not peak for 1-3 days. This leaves a window of time where there may be symptoms of rhabdomyolysis but CK is normal or only slightly elevated. So, a patient might simply be in early rhabdomyolysis, without significantly elevated CK. 

Teaching point: a low CK does NOT rule out rhabdomyolysis. If you are highly suspicious of this diagnosis, go ahead and treat with fluids, electrolyte corrections, and monitor kidney function closely.

As we know, the most immediate risk of rhabdomyolysis is AKI and/or renal failure. To prevent this, we should begin fluid resuscitation of 1-2mL/kg/hr. However, patients with severe rhabdomyolysis and subsequent AKI may need RRT. To find the rights patients who need this immediate intervention, we can risk stratify them into high-risk vs low risk of AKI via the McMohan score (Right):

There is no need to memorize this chart. It is easy to access on MDcalc. 

If the patient has 6+ points, we should consult nephrology and consider RRT, regardless of their CK value.

Treatment and Disposition

  1. Fluid Resuscitation (give IV fluids: either isotonic saline or LR) and Monitor I&O’s). A good starting point is 400ml/hr. 

  2. Electrolyte Management: Check K, Ca, Phos. Also regularly check EKG

  3. Alkalinize urine 

  4. Treat pain with non-nephrotoxic agents. Also discontinue all nephrotoxic or myotoxic medications. 

  5. Consider complications such as compartment syndrome

  6. If McMohan Score is high, but CK is low, this does NOT rule out Rhabdomyolysis. This may be a sign of an early disease course. 

  7. If Mcmohan score <3, CK<5,000, no AKI,  no electrolyte derangements with a normal EKG, and a cause has been identified and stopped, the patient is likely safe for discharge. If any of the above are not met, it may be necessary for admission for supportive measures/treatment.

Key Takeaways

  1. Rhabdomyolysis is the breakdown of muscle tissue which leads to release of intracellular contents into the bloodstream.

  2. Rhabdomyolysis has many causes, including trauma, exercise, and medications

  3. CK is an important lab value, but can lag behind actual clinical symptoms so don’t rely entirely on it. 

  4. Risk stratify your rhabdomyolysis patients for impending renal failure with the McMahan score.

 
 

References:

"McMahon Score for Rhabdomyolysis." MDCalc, www.mdcalc.com/calc/4017/mcmahon-score-rhabdomyolysis#next-steps. Accessed 3 Aug. 2024.

Miller, Andrew. "Rhabdomyolysis: A Comprehensive Review." EMCrit, 2023, https://emcrit.org/ibcc/rhabdo/. Accessed 3 Aug. 2024.

"Rhabdomyolysis: Clinical Manifestations and Diagnosis." UpToDate, 2024, https://www.uptodate.com/contents/rhabdomyolysis-clinical-manifestations-and-diagnosis. Accessed 3 Aug. 2024.

 
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