Exertional rhabdomyolysis: an analysis of 321 hospitalised US military service members and its relationship with heat illness

INTRODUCTION

Exertional rhabdomyolysis is a syndrome of muscle breakdown following exercise. This study describes laboratory and demographic trends of service members hospitalised for exertional rhabdomyolysis and examines the relationships with heat illness.

METHODS

We queried the US Armed Forces Health Surveillance Center's Defence Medical Epidemiology Database for hospitalised cases of rhabdomyolysis associated with physical exertion from January 2010 July 2013. Descriptive statistics reported means and medians of initial, peak and minimal levels of creatine kinase (CK). Correlations explored the relationship between CK, creatinine, length of hospital stay (LOS) and demographic data.

RESULTS

We analysed 321 hospitalised 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 CK levels were significantly lower in heat cases: CK=6528 U/L vs 19 247 U/L, p=0.001; 13 146 U/L vs 22 201 U/L, p=0.03; and 3618 U/L vs 10 321 U/L, p=0.023) respectively, compared with cases of rhabdomyolysis with exertion alone. Median LOS was 2 days (range=0-25). In the rhabdomyolysis with exertion alone group and the rhabdomyolysis with heat group, LOS was moderately correlated with maximal CK (Spearman's ρ=0.52, p<0.001, and Spearman ρ=0.38, p<0.001, respectively). There was no significant difference in median LOS between the rhabdomyolysis with exertion alone and rhabdomyolysis associated with heat groups (2 vs 2, p value=0.96).

CONCLUSION

Most hospitalisations for exertional rhabdomyolysis were associated with heat illness and presented with lower CK levels than cases without associated heat illness. These data add evidence that rhabdomyolysis with heat illness is a different entity than rhabdomyolysis with exertion alone. Differentiating exertional rhabdomyolysis with and without heat should inform future research on rhabdomyolysis prognosis and clinical management.

Causes and outcome of rhabdomyolysis in patients admitted to medical wards in the Prince of Wales Hospital

Background

Rhabdomyolysis with a marked elevation of serum creatine kinase (CK) can be caused by various conditions. Acute kidney injury (AKI) is a potential complication of severe rhabdomyolysis and leads to a rapid increase in serum creatinine.

Methods

This study was performed to identify medical cases diagnosed with rhabdomyolysis and to examine the likely causes. Patients diagnosed with rhabdomyolysis during admission to the medical wards of Prince of Wales Hospital (PWH) in Hong Kong from January 1, 2004 to May 31, 2012 were identified by searching computer records. Details of hospital admissions were retrieved, and the underlying causes of the rhabdomyolysis and clinical outcomes were analyzed.

Results

There were 95 Chinese patients with a median age of 72 years (range, 22–92 years) assigned a diagnosis of rhabdomyolysis. A mild degree of AKI was defined as an increase of serum creatinine more than 20% above the baseline value before onset of acute illness and with the highest creatinine greater than 120 µmol/L. Mild AKI was identified in 63 patients. Rhabdomyolysis appeared to contribute to a fatal outcome in eight patients who had multiple preexisting morbidities. The maximum CK had a median value of 9,829 U/L (range, 472–258,100 U/L). Twelve patients with peak CK levels <10× the upper limit of normal (ULN) may not have had rhabdomyolysis by this standard definition. Of the remaining 83 patients with maximum CK values >10× the ULN, the most common contributing factors were trauma (n=19) and infection (n=17). Other common underlying causes included drug abuse (heroin and alcohol) and ischemia/immobility.

Conclusions

Most patients recovered with appropriate medical interventions and had a median hospital stay of 13 days. One patient was thought to have drug-related rhabdomyolysis due to taking bezafibrate during an episode of renal impairment.

Clinical Practice Guidelines for Exertional Rhabdomyolysis: A Military Medicine Perspective

ABSTRACT

Exertional rhabdomyolysis (ER) is an uncommon condition with a paucity of evidence-based guidance for diagnosis, management, and return to duty or play. Recently, a clinical practice guideline for diagnosis and management of ER in warfighters was updated by a team of military and civilian physicians and researchers using current scientific literature and decades of experience within the military population. The revision concentrated on challenging and controversial clinical questions with applicability to providers in the military and those in the greater sports medicine community. Specific topics addressed: 1) diagnostic criteria for ER; 2) clinical decision making for outpatient versus inpatient treatment; 3) optimal strategies for inpatient management; 4) discharge criteria; 5) identification and assessment of warfighters/athletes at risk for recurrent ER; 6) an appropriate rehabilitative plan; and finally, 7) key clinical questions warranting future research.

Biomarkers, Creatine Kinase, and Kidney Function of Special Operation Candidates During Intense Physiological Training

INTRODUCTION

The purpose of this pilot study was to assess for biomarkers indicative of passing intense physical training and establishing normative values within the tactical athlete population. Unfortunately, none of the biomarkers assessed were indicative of passing training, however, glucose, blood urea nitrogen, and creatine kinase (CK) levels stood out as abnormal. CK levels are commonly used in conjunction with muscle pain and/or myoglobinurea to diagnose exertional rhabdomyolysis (ER) in athletes and the military population. However, research shows that high CK levels may not correlate with acute kidney failure in ER.

MATERIALS AND METHODS

After IRB approval and informed consent, blood samples were obtained from 21 volunteers during two phases of the combat control training pipeline: the first phase (12 participants) was 2 hours of daily physical training followed by 8 hours of academics, and the second phase (nine volunteers) a grueling, 72 hour, intense training cycle (stress inoculation training, SIT) with a historic pass rate of only 50%. Biomarkers were also tracked 48 hours after cessation of SIT.

RESULTS

None of the biomarkers assessed showed a correlation with passing SIT, but high CK levels were well above the diagnostic threshold for ER-as high as 28,000 u/L. At a single point in time, a significant correlation did not exist between CK and others markers associated with rhabdomyolysis. Across time, partial correlations controlling for subject did exist between CK and other markers.

CONCLUSIONS

In our low-powered case control study (pilot study), a nonpathologic elevation of CK is prevalent in high-intensity military training, but not shown to correlate with values associated with acute kidney injury. We assume that real-time collection of these markers could be used once sensors are capable of real-time collection and have the potential for diagnostic affordance. When measured in a between subjects design, our study showed a lack of significance when correlating markers of acute renal injury and elevation of CK. However, when utilized for tracking purposes (within subjects design), the results do show a positive correlation between CK and renal failure biomarkers-specifically only at high physiological stress points.