Comment to Question 2

1.- Non-infectious destructive spondyloarthropathy: A number of musculoskeletal abnormalities may develop in patients who are undergoing HD. Dialysis-related systemic amyloidosis is a serious complication of long-term HD in which ß2-microglobulin has been identified as the major component of the deposited amyloid fibrils. This picture is radiographically characterised by severe narrowing of the intervertebral disc space and erosions and cysts of adjacent vertebral plates with minimal osteophyte formation. The lower part of the cervical spine is more frequently involved than thoracic or lumbar spine. The involvement is generally multivertebral. Neurological deficit is uncommon.
In addition to the ß2-microglobulin level, secondary hyperparathyroidism may play a role in the pathogenesis of destructive spondyloarthropathy. The classic “rugger jersey” spine appearance and disc calcifications, whose appearance suggests apatite deposits due to secondary hyperparathyroidism were not observed in this case, and parathyroid hormone levels were only mildly increased. The duration of ESRD is a major risk factor for both entities.
In summary, the late appearance of these complications, the lack of other classical manifestations, the presence of fever and the radiological findings makes this diagnosis very improbable in this patient.
2.- Metastatic tumour: Several tumours have a tendency to metastasise to the spinal column. Prostate cancer, breast cancer, and lung cancer are the most common but renal cell carcinoma, non-Hodgkin's lymphoma, and multiple myeloma account for 5 to 10 percent of cases.
No constitutional syndrome or other neoplasic signs were found in this case. So far, this diagnosis is less probable but cannot be excluded. In addition, the involvement of disc space is usually lacking in neoplasic lesion of the spine. However, plain radiograph and CT scan are insufficient to establish the diagnosis.
3.- Infectious destructive spondyloarthropathy: The lack of any other antecedent of trauma or cancer and the presence of fever makes the diagnosis of osteomyelitis probable. However, in the previous weeks there was no evidence of any focus of bacteraemia and echocardiography was negative for endocardytis. Further studies are needed to confirm the diagnosis.