A 59-year-old male with a past medical history of hypertension and dyslipidaemia presents with sore muscles, jaundice and oliguria.

The following data are taken from venous blood investigations on his admission:

Parameter

Patient Value

Normal Adult Range

Urea

25.5 mmol/L*

3.0 – 8.0

Creatinine

523 μmol/L*

45 – 90

Sodium

138 mmol/L

134 – 145

Potassium

6.2 mmol/L*

3.4 – 5.0

Chloride

105 mmol/L

98 – 108

Bicarbonate

16 mmol/L*

22 – 32

Calcium (corrected)

2.07 mmol/L*

2.20 – 2.55

Phosphate

1.6 mmol/L*

0.8 – 1.5

Creatine Kinase

60110 U/L*

< 200

Bilirubin

108 μmol/L*

< 20

Alkaline Phosphatase

221 U/L*

35 – 135

Alamine Aminotransferase

1073 U/L*

< 40

g-Glutamyl Transferase

437 U/L*

< 60

Albumin

29 G/L*

35 – 50

a)  What is the diagnosis?

b)  Give four likely causes in this patient.

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College Answer

a) Rhabdomyolysis.

b)

  • Muscle ishaemia / compartment syndrome secondary to peripheral vascular disease
  • Infection
  • Drugs / toxins e.g. statins, alcohol
  • Inflammatory myopathies
  • Endocrine disorders

Discussion

This question could just as easily have been slotted into the electrolyte disturbance section or the renal failure section. The patient plainly has rhabdomyolysis. The college were looking for a single-word answer. The decreased bicarbonate indeed suggests that a metabolic acidosis is in play, and it is a high anion gap sort of thing, with probably some combination of uremic, lactic and normal anion gap acidosis (given that the anion gap is (138) - (105 + 16) = 17, or 23.2 when calculated with potassium, and the delta ratio is (17 - 12) / (24 - 16) = 0.62.)

More interestingly, what could have caused it?

The general breakdown of differentials is as follows:

  • Vascular - muscle ischaemia, eg. ischaemic limb, or myocardial infarction
  • Infectious - eg. necrotising fasciitis
  • Neoplastic , eg. sarcoma
  • Drug-related , eg. due to MDMA or statins, or due to neuroleptic-malignant syndrome
  • Congenital, eg. some sort of congenital myopathy
  • Autoimmune , eg polymyositis or dermatomyositis
  • Traumatic, eg. crush injury, blast injury, compartment syndrome, immobilityetc
  • Environmental , eg. hyperthermic injury, "heat stroke"
  • Endocrine , eg. hyperthyroidism or phaeochromocytoma

Rhabdomyolysis is discussed at greater length in the discussion of Question 16 from the first paper of 2008.

References

References

Allison, Ronald C., and D. Lawrence Bedsole. "The other medical causes of rhabdomyolysis." The American journal of the medical sciences 326.2 (2003): 79-88.