Letters to the Editor

Mild Creatine Kinase Elevations Do Not Necessarily Reflect Rhabdomyolysis


Am Fam Physician. 2021 Jul ;104(1):6-7.

Original Article: Case Reports: Rhabdomyolysis Associated with COVID-19 [Letters to the Editor]

Issue Date: December 1, 2020

See additional reader comments at: https://www.aafp.org/afp/2020/1201/p645a.html

To the Editor: We read with interest the case report by Dr. Singh and colleagues about 10 patients with SARS-CoV-2 infection who developed rhabdomyolysis after the onset of COVID-19. The authors concluded that clinicians should be aware of this life-threatening manifestation of COVID-19 so that prompt and appropriate interventions can be performed.

Having hyperCKemia, which is the elevation of creatine kinase (CK) found in the patients in the case series, does not necessarily reflect rhabdomyolysis in the absence of muscle symptoms. Only three out of 10 patients had myalgias, and only one presented with weakness; it is unclear if it was muscle weakness or generalized fatigue. Nine patients presented with coughing; therefore, it is more likely that the hyperCKemia resulted from overactivity of respiratory muscles than from myositis. HyperCKemia was mild (non–life-threatening), with maximal CK values of less than 10,000 U per L (167.00 μkat per L) in eight patients. Helpful information that would suggest that hyperCKemia originated from skeletal muscles includes the presence of dark (cola-like) urine and myoglobinuria. One patient presented with confusion, and it is crucial to exclude a cerebral cause of hyperCKemia for that patient. COVID-19 can also be complicated by myocarditis, myocardial damage, including myocardial infarction and takotsubo cardiomyopathy, which may have been a source of hyperCKemia.1

Did rhabdomyolysis occur before, together with, or after SARS-CoV-2 infection in the patients? If hyperCKemia occurred before COVID-19, then trauma, epilepsy, tetany, hypokalemia, and compartment syndrome could have been contributing causes.

Several of the drugs commonly used to treat COVID-19 can be myotoxic; therefore, it is crucial to know which drugs the patient received before the onset of rhabdomyolysis. Chloroquine can induce myopathy.2 Azithromycin (Zithromax) can trigger rhabdomyolysis.3 Ritonavir may rarely trigger rhabdomyolysis.4

The authors stated that COVID-19 might be associated with life-threatening complications. Eight of the 10 patients died, but what were the causes of death? Did any of the patients die from complications of rhabdomyolysis? The limitations of this interesting case series should be addressed before accepting the authors' conclusions.

Author disclosure: No relevant financial affiliations.


show all references

1. Gauchotte G, Venard V, Segondy M, et al. SARS-CoV-2 fulminant myocarditis: an autopsy and histopathological case study. Int J Legal Med. 2021;135(2):577–581....

2. Shukla S, Gultekin SH, Saporta M. Pearls & oy-sters: hydroxychloroquine-induced toxic myopathy mimics Pompe disease: critical role of genetic test. Neurology. 2019;92(7):e742–e745.

3. Teng C, Baus C, Wilson JP, et al. Rhabdomyolysis associations with antibiotics: a pharmacovigilance study of the FDA adverse event reporting system. Int J Med Sci. 2019;16(11):1504–1509.

4. Benveniste O, Longuet P, Duval X, et al. Two episodes of acute renal failure, rhabdomyolysis, and severe hepatitis in an AIDS patient successively treated with ritonavir and indinavir. Clin Infect Dis. 1999;28(5):1180–1181.

In Reply: We appreciate the comments by Drs. Finsterer and Scorza. The classic triad of rhabdomyolysis symptoms (muscular aches, weakness, and tea-colored urine) is nonspecific and experienced by less than 10% of patients. More than 50% of patients do not complain of muscle pain or weakness.1,2 Plasma myoglobin is not as sensitive as CK for diagnosis because of a short half-life. Rhabdomyolysis does not always lead to visible myoglobinuria (tea- or cola-colored urine) or may resolve early in the course of rhabdomyolysis.1,2 A systematic review found that in most studies, patients were diagnosed with rhabdomyolysis based on CK levels five times the upper limit of normal (greater than 1,000 U per L [16.70 μkat per L]).1,3 In our case series, the urinalysis obtained at presentation in three patients (cases 4, 5, and 6) showed classic rhabdomyolysis urinalysis findings (moderate blood and 0 to 3 red blood cells [RBCs] per high-power field). One patient (case 10) showed large blood and 4 to 5 RBCs per high-power field. In the other six patients, urinalysis was not obtained or did not show evidence of rhabdomyolysis.

The troponin level obtained at presentation was essentially negative (less than 0.09 ng per mL [0.09 mcg per L]) in all the patients except for case 10, whose troponin level was 0.4 ng per mL (0.4 mcg per L; reference range of less than 0.03 ng per mL [0.03 mcg per L]). In all the patients, CK level was obtained at presentation to the hospital, suggesting a temporal relationship between COVID-19 and rhabdomyolysis. None of the patients had a history of or presented with alcohol or substance misuse, trauma, or exertion. Case 4 had a known history of seizures and was taking antiseizure medications. Only one patient (case 6) had hypokalemia (serum potassium level of 3.1 mEq per L [3.1 mmol per L]) at presentation. None of the patients were taking any of the medications (statins, macrolides) known to cause muscle damage. The patients received chloroquine and azithromycin during their hospitalization for treatment of COVID-19; however, CK levels were already elevated at presentation. A range of potentially life-threatening complications (e.g., acute kidney injury, compartment syndrome, electrolyte imbalance, disseminated intravascular coagulation) have been associated with rhabdomyolysis.2 Further studies are needed for the prognostic value of elevated CK in patients with COVID-19.

Author disclosure: No relevant financial affiliations.


1. Khan FY. Rhabdomyolysis: a review of the literature. Neth J Med. 2009;67(9):272–283.

2. Torres PA, Helmstetter JA, Kaye AM, et al. Rhabdomyolysis: pathogenesis, diagnosis, and treatment. Ochsner J. 2015;15(1):58–69.

3. Chavez LO, Leon M, Einav S, et al. Beyond muscle destruction: a systematic review of rhabdomyolysis for clinical practice. Crit Care. 2016;20(1):135.

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This series is coordinated by Kenny Lin, MD, MPH, Associate Deputy Editor for AFP Online.



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