A 2-year-old female was brought in by parents for a 2-day history of fever, coryza, cough and had been noted to have difficulty walking. This persisted to the point that she had refused to walk for the 4-6 hours prior to ED arrival. She had no significant past medical history and had an unremarkable birth. There was no recent travel and the family history was unremarkable. She weighed 21 kg. In the ED, the child was febrile with a temperature of 102.4 F, heart rate 158, respiratory rate 28 and a pulse ox of 98% room air. No BP was obtained. On exam, she appeared listless, crying at times but consolable. HEENT exam was unremarkable, lungs were clear bilaterally, heart sounds were normal and abdomen was benign. No gross adenopathy was appreciated and no rashes were noted. The musculoskeletal exam revealed good active and passive range of motion of the upper and lower extremities while lying supine. No gross musculoskeletal and joint deformities were noted. No gross joint effusions were noted. Patient cried with any maneuvering or movement. She was placed on her feet and although she stood, she would tend to lean forward, reach for a parent and would refuse to walk.
The initial differential diagnoses included viral syndrome, toxic tenosynovitis, bacterial or septic arthritis, and remotely, trauma. Basic lab studies, urinalysis and radiographic studies were performed, focusing specifically on pelvic and lower extremity radiography. The WBC was 14,800/mcl, the chemistries revealed mild metabolic acidosis with a bicarbonate of 20 mmol/L and an anion gap of 17 mmol/L. Urinalysis revealed large blood on the dipstick but 0-2 rbc/hpf on microscopy. The radiographic studies revealed no fractures and no evidence of joint effusion in the hips. The child was reassessed after the results of the lab studies and antipyretic treatment. Her exam remained unchanged and based on the urinalysis, a serum creatine kinase (CK) level was ordered. The result came back at 24,000 IU/L. The result was confirmed with the laboratory and treatment was initiated for rhabdomyolysis with intravenous hydration, bicarbonate administration and close monitoring of input and output. A pediatric urinary catheter was placed. The child was transferred to a tertiary care facility for definitive care and was diagnosed with viral-induced rhabdomyolysis and treated accordingly. She made a full recovery but unfortunately suffered another bout of the illness 5 months later, developed renal failure and succumbed to her disease.
Rhabdomyolysis is the breakdown of muscle fibers and the leakage of cellular contents into the systemic circulation which can have potentially toxic effects. There are a vast number of causes in the adult population which include trauma, drugs (legal and illegal), burns, exertion etc. The causes in the pediatric population include those of adults but a few unique pediatric causes, including inherited enzyme deficiencies, inherited myopathies, connective tissue disorders and viral myositis. Influenza type B virus is the most common viral agent.
The diagnostic study of choice is a measurement of the CK which will be 5-10 times the normal limit but in early disease may see only a 2-3 times elevation of the CK. The diagnosis can be suggested by a urine dip positive for blood (as a result of hemoglobin and myoglobin leakage) but with no rbc’s on the microscopic study. Complications of rhabdomyolysis include hypovolomia, hyperkalemia, metabolic acidosis, DIC and acute renal failure which can happen in 5% of the population. The overall mortality is roughly 5% also but it depends largely on the cause of the disease.
Treatment largely centers around hydration and the prevention of hyperkalemia and acute renal failure. Vigilant monitoring of the electrolytes, CK level, renal function (monitoring input and output) is required. These patients are best served in an intensive care setting. Obtaining an initial EKG is recommended. Isotonic crystalloid should be administered at a rate sufficient to maintain a urine output of 1-2 ml/kg/hour. Adding bicarbonate when the CK is above 6000 IU/L is also recommended. Adding bicarbonate at a dose of 1 mEq/kg to hypotonic crystalloid and aiming for a urine pH higher than 7 is one such formula. One can also give 2 mEq/kg of bicarbonate every 1-2 hours as needed. Diuretics have also been used to enhance renal perfusion but should not be used until good urine output has been established. This would preclude the use of these agents in the emergency department setting. Hyperkalemia can be treated in the standard fashion. The treatment of other electrolytes such as calcium is usually not warranted.
Rhabdomyolysis is a rare entity in the pediatric population but has a simple test to confirm the diagnosis. Consider this diagnosis next time you have a child who “will not walk”.