Clinical Departments of Nephrology and 1 Radiology, King's College Hospital, London SE5 9RS, UK
Keywords: haemodialysis; magnetic resonance imaging; osteomyelitis
In a series of four haemodialysis patients presenting with chronic backache and episodes of fever and rigor after dialysis, magnetic resonance imaging (MRI) proved to be the key investigation in establishing the diagnosis of osteomyelitis.
MRI is a sensitive method of detecting vertebral body osteomyelitis. There is increased signal on T2W scans and low signal intensity on T1W scans, allowing the full extent of inflammation to be assessed. The sensitivity may be increased by using fat suppression sequences and gadolinium enhancement [1].
Osteomyelitis most commonly occurs in patients with chronic debilitative disease; in our series, three of the four patients had diabetes mellitus. Osteomyelitis is, however, an uncommon sequel of haemodialysis related infection, even in diabetic patients with end stage renal failure.
The axial skeleton is the commonest site of osteomyelitis in adults and this was reflected in our series. This distribution is thought to result from the persistence of cellular rich bone marrow and sluggish, high volume blood flow through the vertebral body. The lumbar vertebrae are the most commonly affected (50%), with preference for the lower vertebrae and contiguous sacrum [2].
Bacterial culture from the four cases grew Gram-negative organisms in one patient, a mix of Gram-positive organisms in two patients, one of which also grew Staphylococcus aureus, and a mix of Gram-negative and S. aureus organisms in the final patient. These results are similar to other reported series, which implicate Gram-negative bacteria in 23% and S. aureus in up to 41% [3].
The incidence of haemodialysis catheter related infection varies in different series from 5.3% to 37% [4] but associated mortality remains low. Controversially, it has been shown that attempted catheter salvage does not increase the probability of complications, leading to the hypothesis that the complication rate is independent of the length of time the catheter remains in situ during antibiotic treatment [5].
In summary, haemodialysis patients are often at risk from the complications of bacteraemia. Back pain and pyrexia should raise suspicion of vertebral body osteomyelitis. MRI, with its high contrast resolution and multi planar imaging capability is ideally suited as the imaging investigation of choice in diagnosing axial skeletal osteomyelitis.
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Notes
Correspondence and offprint requests to: Dr Samantha Negus, FRCR, Department of Radiology, King's College Hospital, London SE5 9RS, UK.
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