The best questions often stem from the inquisitive learner. As educators, we love—and are always humbled—by those moments when we get to say “I don’t know.” For some of these questions, you may already know the answers. For others, you may never have thought to ask the question. For all, questions, comments, concerns, and critiques are encouraged. Welcome to the Kids Korner.

Question

“In children with influenza, muscle pain, and an elevated serum creatine kinase (CK), is there a specific CK level that predicts acute kidney injury or renal failure and warrants admission for continued inpatient hydration?”

It feels like it has been a busier influenza season this year. You may have seen one or two … or a thousand of them. Anecdotally, at our location, it feels like myositis and rhabdomyolysis associated with influenza didn’t really rear its head until later in the flu season. Maybe it was this strain of influenza? Maybe it was our location? Maybe it’s recall bias? Anyway, that association prompted this question.

Rhabdomyolysis is rapid muscle tissue breakdown that results in elevated levels of serum creatine kinase (CK) and can lead to systemic injuries such as acute kidney injury (AKI) and electrolyte imbalances. In adults, there is a scoring system—the McMahon score—that predicts the likelihood of mortality or acute kidney injury (AKI) in patients with rhabdomyolysis patients. The McMahon score incorporates age, sex, and electrolytes abnormalities in addition to CK results.¹

The RIFLE criteria are another system that has been explored to predict the severity and prognosis of AKI in adults.² For children, though, we are unfamiliar with any similar scoring system. The question arises “Is there a particular CK value that predicts an AKI in children with myositis/rhabdomyolysis from influenza?” While every case has other factors that contribute to our decision-making that should be considered, is there a specific CK value that we should really take note of? We’re only seeking to evaluate viral-induced myositis/ rhabdomyolysis and not rhabdomyolysis caused by other etiologies such as trauma or heart disease.

We were unable to find any strong conclusion on a specific CK level or its prognosis for AKI in children. Most pediatric studies on rhabdomyolysis were retrospective, had small numbers, and included variable causes of rhabdomyolysis. For instance, a 2000 retrospective study by Watemberg et al., identified 19 children with rhabdomyolysis over an 8-year period.³ The most common causes were trauma (5), non-ketotic hyperosmolar coma (2), viral myositis (2), dystonia (2), and malignant hyperthermia.² Additionally, the study found that “coma” occurred in seven patients, suggesting an extremely sick patient population. Even with the variation in etiology and severity of illness, though, the authors stated, “There was no significant difference in serum creatine kinase levels in patients with versus without acute renal failure.” However, it is a single small study and thus is difficult to draw any real conclusions.