Meyer-Betz Syndrome

Rhabdomyolysis is seen commonly as a consequence of strenuous exercise. Case reports have included military basic training,² weight lifting,³ and in both recreational and professional marathon runners.⁴
There appears to be an increased risk in patients with sickle cell trait.⁵

Rhabdomyolysis, particularly that associated with exertion, predominantly damages red (type 2) muscle fibres. Myoglobin is released along with other cellular contents after muscle damage and necrosis.

• Normal values for plasma myoglobin concentration are 0 to 0.003 mg/dl.
• The renal threshold for myoglobin is 0.5 to 1.5 mg/dl.
• The urine level of myoglobin must exceed 100 mg/dl before the urine becomes discoloured.
• The serum myoglobin level will rise before serum creatine kinase level. It will rise within hours of onset of injury and return to normal 1- 6 hours after cessation of injury, with rapid renal excretion and metabolism to bilirubin.
• Metabolic acidosis, acute renal failure (ARF), respiratory failure, cardiac arrhythmias and disseminated intravascular coagulation (DIC) all may complicate rhabdomyolysis.

Incidence figures are not available for the general population, but screening of 337 military recruits for myoglobin serum levels, showed rhabdomyolysis in 40%.⁶ It is commoner in men, particularly well-educated professionals, who arrange work schedules to allow for daily running. This lead to the term " white collar rhabdomyolysis".⁷In another series exercise induced rhabdomyolysis accounted for 47% of the admissions with rhabdomyolysis.⁸

Symptoms

The most common symptoms include:

• Muscle pain, weakness, tenderness and stiffness.
• 50% patients present with symptoms in the large muscles of the thigh, calves and the lower back.⁹ Change in colour of the urine, usually to red initially, then brown.
• Constitutional symptoms vary on the cause; the most common are generalised malaise, fever and nausea.
• The associated electrolyte disturbance can lead to agitation and confusion.

Signs

• The affected muscles become swollen and tender on palpation, and occasionally, on beginning fluid therapy, due to extravasation of fluids.
• The muscles involved become stiff and occasionally develop contractures.
• Myoglobinuria
• Tachycardia
• Altered mental state
• Low urine output

• Sickle cell anaemia
• Compartment syndrome
• Disseminated intravascular coagulation
• HIV/AIDS
• Myopathies
• Inborn errors of metabolism:
  • Abnormal carbohydrate metabolism e.g. McArdle disease, Tarui's disease
  • Abnormal lipid metabolism e.g. carnitine deficiency
• Toxicity e.g. drugs of abuse, neuroleptics, SSRIs

• Raised white cell count
• Raised liver function tests
• Features of disseminated intravascular coagulation
• Hypoxia

Diagnosis is made by muscle biopsy, raised creatine kinase and serum myoglobin levels.

General measures

• Input/output chart
• Weighing patient
• Assessment for fluid overload and for onset of acute renal failure (ARF)
• Careful monitoring of pressure within muscle compartments.

Pharmacological

• Hydration:Large quantities of fluid should be given to maintain urine output at 300 ml/hour until the urine is free of myoglobin. The rate of administration depends on the severity of myoglobinuria. Sodium-depleted albumin may be used for volume expansion.
• Alkalinisation of urine with bicarbonate: to prevent dissociation of myoglobin into its nephrotoxic metabolites. Urinary pH should be > 6.5.
• Diuretic therapy: Mannitol and loop diuretics are preferred.
• Treatment for electrolyte disturbance: e.g. hyperkalaemia, hyperphosphataemia.
• Dialysis: may be required in the event of uncontrolled hyperkalaemia, acidosis, fluid overload or uraemic encephalopathy.
• DIC: may require therapy if associated with bleeding.

Surgical

Decompressive fasciotomy may be required to prevent local tissue necrosis.

As previously mentioned:

• Acute renal failure; reports show the incidence of ARF in rhabdomyolysis to range from 17-40%.^10,11
• Respiratory failure
• Cardiac arrhythmias
• Disseminated intravascular coagulation
• Compartment syndrome

If supportive therapy is given promptly, a good recovery can be made.¹²