Meyer-Betz syndrome

What is Meyer-Betz syndrome? (Introduction)

The syndrome of muscle pain, weakness and brown urine was first described in 1910 by Meyer-Betz, a German physician.¹ (NB: there is an alternative attribution in the Concise Oxford Textbook of Medicine to Hans Meyer and Vladimir Betz, although both were deceased by 1895.) In more recent times, it is usually described as idiopathic paroxysmal rhabdomyolysis (a recurring scenario) and is a diagnosis of exclusion.²

Causes of Meyer-Betz syndrome (Aetiology)³

Rhabdomyolysis is seen after strenuous muscular exercise, especially in untrained individuals, lifting heavy weights and performing under scorching hot and humid conditions.

There are two broad categories of causes of rhabdomyolysis; traumatic (or physical causes) and nontraumatic (or nonphysical causes).The other common causes of rhabdomyolysis are trauma (road traffic accidents, crush injury, torture, use of restraints), immobilisation (eg, due to coma), sepsis, and cardiovascular surgery. Many medications have also been implicated; alcohol, colchicine, carbon monoxide, statins, cocaine, corticosteroids, amphetamines, ecstasy, fibrates, diuretics, antimalarials, anticholinergics, intravenous and intramuscular illicit drug use and performance enhancing or weight loss supplements.

There also appears to be an increased risk in patients with haemoglobinopathy eg, sickle cell trait. When all possible causes have been excluded, a diagnosis of Meyer-Betz syndrome can be made.²

Pathogenesis

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.

How common is Meyer-Betz syndrome? (Epidemiology)

Incidence figures are not available for the general population because of the differences in definition for diagnosis and the rarity of the condition, but screening of 337 military recruits for myoglobin serum levels, showed rhabdomyolysis (of whatever type) in 40%.⁴ It is more common in men, particularly well-educated professionals, who arrange work schedules to allow for daily running. This led to the term 'white collar rhabdomyolysis'.⁵

In another series, exercise-induced rhabdomyolysis accounted for 47% of the admissions with rhabdomyolysis.⁶

Signs and symptoms of Meyer-Betz syndrome (presentation)³

Symptoms

The most common symptoms include:

• Muscle pain, weakness, tenderness and stiffness.

• 50% of patients present with symptoms in the large muscles of the thigh, calves and the lower back. 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 - the urine colour is light brown ('tea-coloured').

• Tachycardia.

• Altered mental state.

• Low urine output.

Differential diagnosis³

• Sickle cell anaemia.

• Compartment syndrome.

• Disseminated intravascular coagulation (DIC).

• HIV/AIDS.

• Myopathies.

• Inborn errors of metabolism:
  

  • Abnormal carbohydrate metabolism, eg, McArdle's disease, Tarui's disease.

  • Abnormal lipid metabolism, eg, carnitine deficiency.

• Toxicity, eg, recreational drugs, neuroleptics, selective serotonin reuptake inhibitors (SSRIs).

Diagnosing Meyer-Betz syndrome (investigations)²

• Raised white cell count.

• Raised LFTs.

• Features of disseminated intravascular coagulation (DIC).

• Hypoxia.

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

Management of Meyer-Betz syndrome⁷

General measures

• Input/output chart.

• Weighing the 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: eg, hyperkalaemia, hyperphosphataemia.

• Dialysis: may be required in the event of uncontrolled hyperkalaemia, acidosis, fluid overload or uraemic encephalopathy.

• Disseminated intravascular coagulation (DIC): may require therapy if associated with bleeding.

Surgical

Decompressive fasciotomy may be required to prevent local tissue necrosis.

Complications of Meyer-Betz syndrome⁷

As previously mentioned:

• Acute kidney injury (AKI); reports show the incidence of AKI in rhabdomyolysis to range from 17% to 40%.⁸

• Respiratory failure.

• Cardiac arrhythmias.

• Disseminated intravascular coagulation (DIC).

• Compartment syndrome.

Prognosis

If supportive therapy is given promptly, even when AKI ensues, a good recovery can be made.⁹