Now on to some pediatric studies specifically in the ED setting. The first was an eight-year retrospective study at two Italian pediatric EDs and included 113 children ages 2 to 13.2 years old (median 6 years old).⁹ Specifically, the authors were interested in evaluating benign acute childhood myositis (BACM)—which is a viral-induced myositis that typically affects the calves and is associated with an elevated serum CK level. This is the group that we are specifically interested in with our question today. The most common viral illness in the study was influenza. Children were hospitalized in 85 percent (96/113) of the cases in this study. No one required dialysis or had significant electrolyte abnormalities observed during their admission. The median age was 6 years old and the median serum CK level at admission was 1,413 IU/L with a range of 257 to 12,858 IU/L. That’s a large range of serum CK values but all children had a benign course and excellent clinical outcome. Another 2018 retrospective study of 54 children with benign acute childhood myositis had similar results (n=54).¹⁰ The mean age was 7.4 years old with a mean initial CK of 1,872 I/U (median 2207 IU/L) at admission. No patients developed an AKI or developed renal failure. In this study, an AKI was defined as an increase in serum Cr concentration of 50 percent or more from baseline. Again, this study supports a benign disease process where there is no particular CK cut-off value that suggests concern for the development of an AKI or renal failure. The highest serum CK in the study was 8,086 IU.

Conversely, though, a final study of benign acute childhood myositis suggests a different outcome.¹¹ It was a four-year retrospective study that included 114 children with a median age of 7 years old. The median CK was 3,332 IU/L (range 427 to 50,185). Unlike the prior studies, two of these patients did develop acute renal failure and the study only admitted 23 percent of the patients. All patients in the ED got IV fluid rehydration and alkalization of urine—which may not regularly happen in all ED settings. Acute renal failure occurred in two patients who both demonstrated serum CK levels greater than 20,000 IU/L. Both these patients reportedly appeared sick. In general, this does suggest that, overall, the disease is benign—but acute renal failure can and does occasionally occur.

Summary

There is no specific elevated CK value in viral-induced myositis/rhabdomyolysis that suggests the development of acute renal failure. Many children develop elevated CK levels in the 3,000 IU/L range with good outcomes. The overall clinical picture of the patients appears to be the best indicator. Myositis associated with elevated CK levels in the setting of viral illnesses (particularly influenza) is referred to as Benign Acute Childhood Myositis. Acute renal failure can occur, but it is very uncommon.