AL amyloidosis presenting as inflammatory polyarthritis: a case report

Amyloidosis is a condition characterised by extracellular tissue deposition of fibrils causing a wide range of clinical manifestations. This protein deposition can occur in any tissue, most commonly in the kidney, heart, skin, peripheral nervous system, and gastrointestinal tract. However, the deposition of amyloid fibrils in the synovium is seldom reported. Musculoskeletal manifestations are subtle, subclinical and rarely the patient presents with symptoms that resemble rheumatic diseases. Here, we describe a 55-year-old man with AL (amyloid light chain) amyloidosis who presented with inflammatory polyarthritis with significant morning stiffness, inflammatory low back pain, and painful thickened tongue. The patient had anaemia, macroglossia with lateral scalloping of the tongue, papules, and plaques in the periocular, perioral and perinasal area, bilateral carpal tunnel syndrome, localised soft tissue swelling over the joints, restricted movement in different joints with flexion contractures in some joints. Rheumatoid factor and ACPA were negative and the X-ray of the sacroiliac joints was normal. We confirmed amyloidosis by biopsy of an affected skin lesion. In the urine, no Bence Jones protein was found and bone marrow study and x-ray of the skull were normal. Plasma immuno-electrophoresis and serum free light chain (FLC) assay confirmed lambda light chain type monoclonal gammopathy. Take home message: Although AL amyloidosis is a rare condition, it should be considered while evaluating atypical symptoms in patients presenting with rheumatic complaints. A high index of suspicion is necessary for proper diagnosis as delay in diagnosis will yield a poorer treatment outcome.