Prevalence of subclinical amyloidosis in ankylosing spondylitis

To study the prevalence of secondary amyloidosis in Indian patients with ankylosing spondylitis (AS).

Seventy-two AS patients with disease duration of more than 5 years were included in this study over a period of one and a half years. Abdominal subcutaneous fat pad aspiration (ASFA) was performed with a fine needle, and smears were examined for apple-green birefringence under polarized light after Congo red staining. The amyloid deposits were graded from 1+ to 3+ by visual inspection. Clinical and laboratory features of the patients were correlated with the absence or presence of amyloid deposits.

Five patients (6.9%) with AS were positive for amyloid on ASFA. All the patients had 1+ deposit and were male. None of the patients had clinical amyloidosis. ASFA positive patients had a trend towards older age, longer disease duration, more limitation of the spinal mobility, and significantly lower hemoglobin levels.

We found in our population that subclinical amyloid deposits can be detected in 7% of AS patients with disease duration longer than 5 years. There is a need to follow up patients with positive ASFA tests to check for the development of clinical amyloid.