In our Morning Report at WCH this week, we discussed an approach to the evaluation of myalgias and elevated creatine kinase (CK) levels.
Learning Points:
- Causes of myalgias
- Differential diagnosis of rhabdomyolysis
- Preliminary work-up
- Electrolyte disturbances seen in rhabdomyolysis
- Management basics for rhabdomyolysis
Differential Diagnosis of Myalgias:
- may be focal or generalized
- focal: trauma, pyomyositis, myofascial pain syndrome, muscle infarction, compartment syndrome
- generalized:
- Infection
- Autoimmune: PMR, Poly/dermatomyositis, RA, SLE, Spondylarthropathy
- Endocrine: Hypothyroidism, Adrenal insufficiency
- Medication: statins, many others
- Psychiatric
- Noninflammatory pain syndromes: Fibromyalgia, Chronic Fatigue Syndrome
Differential Diagnosis of Rhabdomyolysis:
- Rhabdomyolysis = muscle necrosis + release of intracellular components from within muscle
- kind of like “tumor lysis” but from a muscle!
- Physiology is similar:
- Release of K, phosphate, uric acid, LDH
- Also release of myoglobin which does not have a binding-molecule like hemoglobin (haptoglobin)
- Physiology is similar:
- kind of like “tumor lysis” but from a muscle!
Suggested preliminary investigations:
- For the evaluation of a muscle complaint or suspected rhabdomyolysis:
- CBC (look for infection)
- Coagulation markers (DIC may coexist)
- Lytes, Extended lytes, Uric Acid
- AST, ALT, ALP, Tbili with LDH and CK, trop
- Creatinine, urea, urinalysis, urine myoglobin
- Urine microscopy-hemegranular (‘muddy brown’) casts in acute tubular necrosis (ATN)
- Tox screen
- Consider ESR, CRP, ANA, ENA (anti Jo-1)
- Pertinent infectious work-up if suspected (i.e. Throat swabs, NP swab, blood cultures, sputum, etc)
Electrolyte abnormalities in rhabdomyolysis:
Management Principles:
- Major therapeutic aims:
- target and maintain euvolemia
- Prevent/limit renal injury relating to myoglobinuria
- IV fluid resuscitation
- increasing urine output limits cast formation and promotes potassium excretion
- can consider use of sodium bicarbonate infusion to achieve forced alkaline diuresis (pH>6.5) though there is no clear evidence of benefit
- Bicarb infusion ‘recipe’: 3 amps of NaHCO3 in 850 cc of D5W
- Diuretics
- theoretically to enhance urine output and prevent precipitation in renal tubules
- Neither mannitol or lasix of clear-evidence of benefit
Additional Clinical Pearls:
- Influenza is a common cause of elevated CK levels/myositis
- A positive urine dip for blood but absence of red blood cells on urine microscopy is suggestive of myoglobinuria
- Elevated CK levels can be multifactorial; an inciting trigger (drug/infection) might unmask an underlying muscle/mitochondrial disorder
Further Reading:
- Chatzizisis, YS et al. The syndrome of rhabdomyolysis: Complications and treatment. European Journal of Internal Medicine. 2008; 19:568-574.
- Giannoglou, GD. The syndrome of rhabdomyolysis: Pathophysiology and Diagnosis. European Journal of Internal Medicine. 2007; 18: 90-100.