Climate Change Might Make Condition More Common
Earlier this year, recruits perform a physical training session outside at Recruit Training Command. A new study looks at exertional rhabdomyolysis and its relationship with heat illness. U.S. Navy photo by Mass Communication Specialist 2nd Class Christopher M. O’Grady
SEATTLE — Most hospitalizations in military servicemembers for exertional rhabdomyolysis, a syndrome of muscle breakdown following exercise, are associated with heat illness and present with lower creatine kinase levels than cases without associated heat illness, according to a recent study.
The cross-sectional study published in the journal BMJ Military Health describes laboratory and demographic trends of servicemembers hospitalized for exertional rhabdomyolysis and examines the relationships with heat illness. It is the largest descriptive study of exertional rhabdomyolysis that explores the relationship between heat, exertion, creatine kinase levels and length of hospital stay.1
Exertional rhabdomyolysis is poorly understood, and little is known about its prognosis and optimal hospital management, especially between exertional rhabdomyolysis with and without heat-related illness, according to authors. Differentiating exertional rhabdomyolysis with and without heat is expected to provide beneficial information for future research on rhabdomyolysis prognosis and clinical management.
The current study queried a database of all U.S. servicemembers in the U.S. Armed Forces Health Surveillance Center’s Defense Medical Epidemiology Database, and keyed in on hospital diagnosis of rhabdomyolysis, physical exertion and heat illness. The query found 321 cases of servicemembers hospitalized for exertional rhabdomyolysis over 2½ years, from January 2010 to July 2013.
“Of all the cases of exertional rhabdomyolysis that were hospitalized, we found that the majority of cases (60%) were associated with heat illness,” Robert Oh, MD, MPH, associate chief of staff for education at the VA Puget Sound Health Care System in Seattle, told U.S. Medicine. “Those that were admitted for rhabdomyolysis with just exertion alone had higher levels of creatine kinase (a blood marker of muscle breakdown).”
“Our study suggests that exertional rhabdomyolysis associated with heat illness may be a distinct entity than the muscle breakdown related to exercise. We need more studies to determine if they are managed differently and how that relates to health and long-term effects,” he said.
Exertional rhabdomyolysis, the breakdown of skeletal muscle as a result of vigorous physical training, work or exercise, is more common in physically active populations such as military servicemembers and athletes. The intense physical training and occupational demands of military servicemembers place them at higher risk of exertional illness and injury.
Related sequelae for this serious and potentially fatal condition include acute kidney injury, myoglobinuria, compartment syndrome, electrolyte abnormalities and coagulopathy. Diagnosis is made when there is laboratory evidence of myonecrosis following excessive physical activity. Rhabdomyolysis is generally associated with creatine kinase at least five times the upper limit of normal, which reflects significant muscle breakdown.
Hospitalization is often recommended for severely elevated creatine kinase levels or the presence of high-risk markers including myoglobinuria, acute kidney injury, elevated troponin or other metabolic abnormality.
Among the 321 hospitalized cases of exertional rhabdomyolysis, 193 (60.1%) cases were associated with heat; 104 (32.4%) were not associated with heat; and 24 (7.5%) were classified as medical-associated exertional rhabdomyolysis. Initial, maximum and minimal creatine kinase levels were significantly lower in heat cases, compared with cases of rhabdomyolysis with exertion alone. The median length of hospital stay was two days.
“We know with climate change that heat-related illnesses will continue to be a problem, especially with active people who work and train outside,” Oh wrote in an email. “In our study, exertional rhabdomyolysis associated with heat appears to be managed differently than those associated with exertion without a heat illness. This matters clinically, since it is important to differentiate rhabdomyolysis if associated with a heat illness versus exercise alone, as they may be managed differently, as it suggests in our research.”
It’s important to distinguish if the rise of creatine kinase is due to exercise itself or if this is in relationship with a concomitant heat illness, Oh added.
“In my clinical experience in the military, we treated the heat illness primarily and any muscle breakdown we felt it was secondary to the treatment of the heat illness (such as heat stroke),” Oh explained in an email. “We also found that the muscle breakdown (creatine kinase) levels related to exercise alone tend to be higher, but there wasn’t any difference in length of stay. This also suggests that treatment of the muscle breakdown due to exercise alone was the primary issue and may be managed differently in the hospital setting.”
Oh believes, that researchers need to look at heat illness and treat the secondary effects (muscle breakdown, liver abnormalities) differently than those related purely with exercise alone.
“This also suggests that exertional rhabdomyolysis associated with just exercise alone may have a more favorable prognosis, and we need to determine through further research what elevated levels of creatine kinase mean for long term participation in the military and for overall health,” Oh wrote in an email.
Among limitations of this study, there is no ICD-9-CM code for exertional rhabdomyolysis, so inclusion and exclusion criteria were used to help distinguish exertional cases from other causes of rhabdomyolysis. Also, this study was based on U.S. service members and may not be generalizable for other populations.
- Oh RC, Bury DC, McClure CJ. Exertional rhabdomyolysis: an analysis of 321 hospitalised US military service members and its relationship with heat illness. BMJ Mil Health. 2022 Nov 28:e002028. doi: 10.1136/military-2021-002028. Epub ahead of print. PMID: 36442890.
