INTRODUCTION
Amyloidosis refers to the extracellular tissue deposition of fibrils that are composed of low-molecular-weight subunits derived from a variety of serum proteins. Amyloid deposits can occur in a variety of organs, with morbidity and mortality often related to the involvement of the heart, kidney, gastrointestinal tract, and nervous system. (See "Overview of amyloidosis".)
Different types of amyloidosis are derived from various fibril subunit proteins, as summarized in the table (table 1). As an example, immunoglobulin light chain (AL) amyloidosis is derived from monoclonal immunoglobulin light chains and/or light-chain fragments (which may be a complication of plasma cell dyscrasias), while AA amyloidosis is derived from a fragment of serum amyloid A (SAA) protein (whose production is driven by an underlying chronic inflammatory disorder). The most common forms of systemic amyloidosis with musculoskeletal manifestations are outlined in the table (table 2).
A variety of amyloid types are associated with musculoskeletal symptoms, including AL amyloidosis, transthyretin (TTR) amyloidosis (ATTR), and dialysis-related amyloidosis (DRA). The type of amyloidosis will drive the subsequent treatment strategy and can be distinguished with immunohistologic, biochemical, and or mass spectrometry studies [1].
Musculoskeletal manifestations of amyloid deposition may be subtle, subclinical, and only apparent when a tissue biopsy is carried out in AL and AA amyloidosis, but their prevalence is increasingly recognized in ATTR [2]. Rarely, patients present with a clinical picture that simulates a known rheumatic disease [3-5]. In addition, rheumatic diseases with musculoskeletal symptoms can cause AA amyloidosis. (See "AA amyloidosis: Causes and diagnosis".)
This topic will review the musculoskeletal manifestations of the various forms of amyloidosis. Other organ-specific manifestations of amyloidosis are discussed separately:
