Exertional rhabdomyolysis (muscle damage from overexertion exercise) has been reported in many case studies of otherwise healthy individuals. Some of the first reports described incidents that occurred during military training (1,6,10,11,14,25), but also other reports exist of rhabdomyolysis induced by recreational exercise (12,13,24,27,33). We recently noted two cases where healthy adults were encouraged to perform excessive strenuous exercise in a health club setting, which led to hospitalization to prevent renal failure (29). Renal failure develops because myoglobin released from damaged muscle into the circulation can precipitate in the kidney, obstruct the renal tubules, lead to tubular necrosis, and effectively shut down the kidneys (16,17,26).
In all reported cases of exertional rhabdomyolysis, subjects have been adults or older teens. Chamberlain (2) noted an incidence of 7rhabdomyolysis of 0.26% in children from 8 to 18 yr of age; however, none of these cases involved healthy children exposed to exercise. One published case report of exertional rhabdomyolysis in a young person described a 17-yr-old boy who presented with myalgia, weakness, and dark urine 6 d following the start of high-school football practice (22). Myalgia was first noted on the evening after the first practice, but the boy continued the practice sessions for the next 5 d. Serum creatine kinase (CK) was 96,000 U·L−1 and urine dipstick was positive for the presence of blood. Serum potassium, creatinine, and blood urea nitrogen (BUN) were 6.0 mEq·L−1, 3.9 mg·dL−1, and 51 mg·dL−1, respectively. To reduce the hyperkalemia, the patient was treated with intravenous insulin, glucose, and calcium gluconate, inhaled nebulized albuterol, and oral sodium polystyrene sulfonate. Intravenous sodium bicarbonate was administered to alkalinize the urine. Seven days later, the patient was released from the hospital. Lin et al. (18) presented a brief report of 119 high-school students aged 17-18 yr who performed 120 push-ups in 5 min as part of a physical education class. The serum CK values ranged from 55 to 174,260 U·L−1. Many of the students developed muscle pain and dark urine 2-4 d after the exercise. Most were treated as outpatients with oral hydration, but 20 students were admitted to the hospital and were later discharged without organ damage.
Here, we present a case of exertional rhabdomyolysis in a boy 12 yr of age, the youngest case of exertional rhabdomyolysis ever reported. Details of the precipitating exercise event and actual hospital records were provided by the boy's parent with the understanding that the information would be used for publication without identifiers.
A white boy 12 yr of age presented to the emergency room with a chief complaint of severe muscle soreness and brown urine. Two days before admission, the boy participated in an athletic physical education class at 1300 h, where the physical education teacher had the class perform between 250 and 500 successive, rapid squat-jumps instead of regular weight training as a penalty for misbehaving in class (talking and not paying attention when the coach was speaking). The squats were full deep knee bends onto the toe followed by jumping up from that position while keeping the hands laced behind the head. The students also performed push-ups that were alternated with the squat-jumps. The total exercise time was estimated to be approximately 25-30 min. In querying the boy's parent, it seemed that heat stress was not a factor; the exercises occurred indoors. The boy remained asymptomatic the rest of the day. The morning of the next day the boy was very sore; he could hardly get out of a chair and began to cry because of the difficulty in moving. The soreness continued the following day (2 d postexercise) with stiffness that made walking difficult, and he needed help to get dressed. At 2200 h that evening, the child reported brown urine, and his parent took him to the emergency room at a local hospital. On the day before the emergency room visit, the boy had taken four 160-mg junior Tylenol, and repeated the same dosage of this medication earlier in the day of this emergency hospital visit (2 d postexercise).
Prior to the incident, the boy had been regularly playing football and basketball and had never experienced any related remarkable problems with exercise. He was otherwise healthy with no allergies. According to his parent, the boy reportedly had not used dietary supplements. Family history noted protein C and protein S deficiency. The boy had a sore throat about 1 wk prior to the exercise event. He had grown 8.2 cm in the past 8 months.
The emergency intake records noted that temperature, heart rate, respiratory rate, and blood pressure were 36.6°C, 78 bpm, 18 breaths per minute, and 123/72 mm Hg, respectively. The boy's height and weight were 170.8 cm and 52.3 kg, respectively. Blood and urine samples were taken immediately by the triage nurse at approximately 2330 h. Emergency room urinalysis results are presented in Table 1. His serum CK was 92,115 U·L−1 (CK-MB 37.1 ng·dL−1) and his alanine transaminase (ALT) and aspartate aminotransferase (AST) were 368 U·L−1 and 1520 U·L−1, respectively. Other blood chemistry and electrolyte profiles were unremarkable. Red blood cell amount (5.46 million per microliter), hemoglobin (Hb) (16.3 g·dL−1), hematocrit (Hct) (47.0%), and mean corpuscular Hb (29.8 pg per cell) were elevated above normal, indicating hemoconcentration. The automated differential showed 54% neutrophils and 10% monocytes, both above normal.
The patient was transferred to another hospital at 0330 h, 3 d postexercise. His temperature was 37.1°C, heart rate 77 bpm, respiratory rate 20 breaths per minute, and blood pressure 155/87 mm Hg. Complete blood count was assessed at 3 and 5 d postexercise. At 3 d postexercise, segmented neutrophils were 74% (normal 23-61%), lymphocytes were 16% (normal 28-65%), and monocytes were 6% (normal 0-5%). Other counts were within a normal range. At 5 d postexercise, segmented neutrophils were 63%, and other counts were within the normal range. His hospital entry urinalysis results are presented in Table 1. No crystals, casts, or bacteria were observed. The urine, however, was myoglobin and Hb positive. Serum measures at hospital entry and over the 7 d of hospitalization are presented in Table 2. In addition, normal values for serum magnesium, calcium, uric acid, and phosphorus were determined at entry. An infectious disease specialist at the hospital was consulted because it was thought that viral infection may have contributed to the severe rhabdomyolysis. Assessments were done for possible viral cause, including tests for Epstein-Barr virus, cytomegalovirus, mycoplasma, influenza, and other viruses that all were negative. Tests for protein C and protein S deficiency also proved negative.
The boy received intravenous (IV) fluids with 5% glucose, 1/4 normal saline with 30 mEq sodium bicarbonate per liter with 2 mEq KCl in 100 mL·h−1 in the emergency room, and 30 mEq sodium bicarbonate and 2 mEq KCl·100 mL−1 during his hospitalization. The boy was discharged after 7 d of hospitalization, and CK was 9101 U·L−1 at this time.
This is the first report of exertional rhabdomyolysis in a young child (preteen). The precipitating event was overexertion exercise encouraged by a physical education instructor. The exercise consisted of repetitive squat-jumps estimated to be somewhere between 250 and 500, with the exact number unknown because the count would restart if any child was caught performing them incorrectly. The boy's parent reported anecdotally that other students in class were not hospitalized, but three noted dark urine and one of these students had a blood CK of 5000 U·L−1 about a week after the incident. The squat-jump exercise includes a strong eccentric (muscle lengthening) component. Stretching the muscle while it is attempting to contract creates a strain on the muscle fibers that results in disrupting the sarcomeric structures of the fiber (23).
Although numerous studies exist showing that exercises biased toward eccentric contractions result in muscle damage (3-5), these studies have examined adults. The few studies of the effects of eccentric exercise in children have either shown no difference or less damage in children compared with adults. Webber et al. (32) reported that the development of muscle soreness and damage (as assessed by increases in serum CK activity) after a downhill run was similar between children and adults. Two other studies, however, showed that children suffered less damage in response to resistance exercise (28) and squat-jumps (19). The latter study (19) is particularly germane to this case report because similar exercises were performed. In that study, 10 boys aged 9-10 yr and 10 men aged 20-29 yr performed 80 squat-jumps, and peak soreness after exercise was approximately two thirds less for the boys. In fact, soreness for the men increased at 24 h postexercise, the soreness for the boys decreased at the same time point. A greater strength loss occurred for the men and slower recovery, such that strength was not restored at 72 h postexercise for the men, but fully restored at 48 h for the boys. The authors suggested that (a) children are more flexible and therefore would not experience as much strain on the sarcomeres as would adults, (b) children may be more physically active than adults, and (c) children may rely more on slow twitch fibers than adults.
The fact that laboratory reports show that children experience less damage than adults in response to strenuous exercise (19,28) and that no reports exist of exertional rhabdomyolysis in young children, makes this case particularly unique. Why this child, and not others in the same class, suffered extreme muscle damage in response to the exercise is puzzling. The hospital examination and laboratory reports of this case study show no unusual predisposing factors. The boy did not take nutritional supplements or regularly take medication. He did, however, take acetaminophen on the second day postexercise. Acetaminophen is commonly used to reduce muscle pain, but in rare situations has been associated with renal failure (8). It is tempting to speculate that the combination of severe muscle damage, large amount of myoglobin in the blood, hemoconcentration, and use of acetaminophen increases the likelihood of compromised renal function in children with exertional rhabdomyolysis, but this warrants further study.
The parent stated that the only difference she noted in her son versus the other boys in the class was that during the past few months, the boy had grown quite a bit taller. He had grown 8.2 cm in 8 months (12.3 cm·yr−1), which is a little higher than the peak height velocity of about 9-10 cm·yr−1 reported for boys between the ages of 13 and 14 yr (9,21,30,31). During the adolescent growth spurt, the long bones grow faster than muscle (15), which may make the muscle more susceptible to strain induced by forceful eccentric muscle contractions. Muscles exercised at a longer length produced more muscle damage than muscles exercised at a shortened length (23). During rapid growth, the muscle is stretched and may be transiently less flexible and stiffer. Feldman et al. (7) compared changes in height with changes in flexibility after 6 and 12 months in students about 14 yr of age and found no relationship. Micheli (20), however, noted that a 6-month interval may be too long to capture the growth spurt and that the growth spurt generally occurs before age 14, so that Feldman et al. may have missed it. The "Micheli" hypothesis suggests a transient loss in flexibility that coincides with the peak growth and that this may be an additional risk factor for overuse injury (20). The risk of injury increases in muscles that undergo eccentric contractions during sports activities. Thus, in the present case, the boy had experienced rapid growth, and it is likely his muscles were less flexible and more susceptible to damage from the stretch of the eccentric contractions.
In summary, a healthy, active boy 12 yr of age was hospitalized with severe exertional rhabdomyolysis after participating in a physical education class where 250-500 squat-jumps were performed as penalty for misbehaving in class. That this child had recently experienced rapid growth could have predisposed him to a greater risk of injury from eccentric muscle-lengthening contractions. The growth spurt may be a particularly vulnerable time for performing exercises that are biased toward eccentric contractions because of the stretch placed on the muscle from growing bones. Physicians should look for signs of exertional rhabdomyolysis in children who have unexpectedly high exercise volume, especially during or immediately following the growth spurt. Physical education and coaching curriculums should incorporate educational material on the potential danger of excessive exercise in children.
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