A 55-year-old men is diabetic and has a long history of renal failure. He is currently waiting for an organ for transplant and has been on hemodialysis in the interim. If this man develops amyloid deposits around his joints, they are likely to be composed of which of the following substances?
**Core Concept**
Amyloid deposits are abnormal protein aggregations that can accumulate in various tissues, leading to disease. In patients with chronic renal failure, particularly those on hemodialysis, secondary amyloidosis can occur. This condition involves the deposition of amyloid fibrils composed of a specific protein.
**Why the Correct Answer is Right**
The correct answer is transthyretin (TTR). In patients with chronic renal failure, particularly those on hemodialysis, secondary amyloidosis can occur due to the accumulation of TTR amyloid fibrils. TTR is a transport protein that normally carries thyroxine and retinol (vitamin A) in the blood. However, in the setting of chronic inflammation and oxidative stress associated with renal failure, TTR can misfold and form amyloid fibrils, leading to the deposition of amyloid around joints and other tissues.
**Why Each Wrong Option is Incorrect**
**Option A:** Although beta-2 microglobulin amyloidosis can occur in patients on long-term hemodialysis, it typically affects the bones and joints, but the amyloid deposits are usually composed of beta-2 microglobulin, not transthyretin.
**Option B:** No information is available about the amyloid deposits in this man being composed of immunoglobulin light chains (AL amyloidosis), which is a primary amyloidosis associated with plasma cell dyscrasias.
**Option C:** No information is available about the amyloid deposits in this man being composed of apolipoprotein A-I (AA amyloidosis), which is a primary amyloidosis associated with chronic inflammatory conditions.
**Clinical Pearl / High-Yield Fact**
Secondary amyloidosis in patients with chronic renal failure is often associated with long-term hemodialysis and can affect multiple organs, including the joints, liver, spleen, and kidneys. Recognizing the risk factors and clinical presentation of secondary amyloidosis is essential for early diagnosis and treatment.
**Correct Answer: C. Transthyretin.**