Amyloidosis is a group of conditions in which misfolded proteins build up in organs and tissues, gradually interfering with how they work. The symptoms depend heavily on which organs are affected, but the most common ones involve the heart, kidneys, nerves, and liver. Because the disease mimics many other conditions, it’s frequently misdiagnosed for years before the real cause is identified.
More than 30 different proteins can misfold and cause amyloidosis, but two types account for most cases. AL amyloidosis (light chain) involves abnormal antibody fragments produced by bone marrow cells. ATTR amyloidosis involves a liver protein called transthyretin. Both are rare: AL amyloidosis affects roughly 17 per million adults per year in the United States, with an overall prevalence of about 69 per million.
How Amyloid Deposits Damage Organs
Normally soluble proteins misfold into sticky, sheet-like structures that clump together. These clumps grow into tiny fibers called fibrils, just 4 to 13 nanometers wide, that weave into organ tissue. Once embedded, the fibrils physically disrupt the organ’s architecture. A heart stiffened by amyloid can’t relax properly between beats. A kidney clogged with deposits leaks protein into the urine. The damage is cumulative: the longer the deposits go undetected, the more organ function deteriorates.
Amyloid deposits can be localized to a single site, as in Alzheimer’s disease, or systemic, meaning they spread through multiple organs at once. Most forms that cause the symptoms described below are systemic.
Heart Symptoms
The heart is one of the most commonly and seriously affected organs, particularly in both AL and ATTR amyloidosis. Amyloid deposits stiffen the heart walls, making it harder for the chambers to fill with blood. This leads to heart failure, often the type where the heart pumps with normal strength but can’t relax enough to fill properly.
Symptoms to watch for include shortness of breath during activity or even at rest, fatigue that worsens over time, swelling in the legs and abdomen from fluid buildup, and difficulty lying flat at night without feeling breathless. Heart rhythm problems are also common, causing lightheadedness, dizziness, palpitations, and fainting episodes. In ATTR amyloidosis specifically, atrial fibrillation and abnormally slow heart rhythms are frequent, sometimes requiring a pacemaker.
Amyloid can also deposit directly in heart valves, causing them to leak or narrow. ATTR amyloidosis has been found in a notable number of older patients being treated for severe aortic valve narrowing, suggesting the two conditions overlap more than previously recognized.
Nerve Symptoms
Nerve damage is a hallmark of ATTR amyloidosis, though it occurs in AL amyloidosis as well. It typically starts in the small nerve fibers of the feet and works its way upward. Early symptoms include pain, tingling, or numbness in the feet, gradually progressing to the hands. Over time, muscle weakness develops in the legs and arms, leading to difficulty walking, balance problems, and falls.
The autonomic nervous system, which controls involuntary functions, is often hit hard. This causes a cluster of symptoms that can be confusing on their own: dizziness or fainting when standing up (from blood pressure dropping), chronic diarrhea or constipation that alternates unpredictably, and erectile dysfunction. Unexplained weight loss frequently accompanies these neurological symptoms.
Kidney and Liver Symptoms
When amyloid deposits infiltrate the kidneys, the most characteristic sign is protein spilling into the urine. You might notice foamy or frothy urine. As protein loss increases, the body retains fluid, causing swelling in the legs, ankles, and around the eyes. Severe cases progress to nephrotic syndrome, defined by very high protein loss (more than 3.5 grams per day) along with low blood protein levels.
Liver involvement usually shows up as an enlarged liver, which a doctor may notice during a physical exam or on imaging. Most people with hepatic amyloidosis don’t feel dramatic liver symptoms early on. The liver may enlarge substantially before causing noticeable discomfort, and standard liver blood tests can sometimes remain close to normal even with significant amyloid burden.
Skin and Tongue Changes
AL amyloidosis produces some of the most visually distinctive signs of any form of the disease. Purpura, or small patches of bleeding under the skin, is a hallmark. These purple or reddish spots tend to appear around the eyes, on the neck, and in skin folds like the armpits. A characteristic pattern called “pinch purpura” occurs when even light pinching or minor bumps cause bruising, because amyloid weakens the walls of tiny blood vessels.
Other skin findings include waxy, translucent bumps that cluster in flexural areas such as the neck, armpits, and groin, along with a darkening of the skin over the upper trunk and around the eyes.
Macroglossia, or an enlarged tongue, is one of the most specific signs of AL amyloidosis, though it only occurs in about 15% of cases. The tongue swells from amyloid depositing in its tissue, which can interfere with speech and eating. When present, it’s a strong diagnostic clue.
Early Signs That Get Misdiagnosed
One of the most frustrating aspects of amyloidosis is how often its early symptoms are attributed to something else entirely. Bilateral carpal tunnel syndrome, meaning both wrists are affected, can precede an amyloidosis diagnosis by years. So can spinal stenosis in the lower back. In ATTR amyloidosis, a history of surgically corrected bilateral carpal tunnel or lumbar stenosis that failed to fully resolve is considered a red flag.
Nerve symptoms are frequently misdiagnosed as diabetic neuropathy, chronic inflammatory nerve disease, or simply “neuropathy of unknown cause.” The key distinguishing features that should raise suspicion include worsening upper limb symptoms despite carpal tunnel surgery, nerve symptoms that keep progressing despite treatment for the presumed diagnosis, and the combination of nerve problems with any autonomic symptoms like digestive issues, dizziness on standing, or unexplained weight loss.
Heart-related amyloidosis is commonly mistaken for ordinary heart failure or age-related heart thickening, especially in older adults. Expert consensus recommendations now suggest screening for ATTR amyloidosis in older adults who have bilateral carpal tunnel syndrome alongside heart failure with preserved pumping strength or unexplained thickening of the heart muscle.
How Amyloidosis Is Diagnosed
Diagnosis typically starts with a tissue biopsy. A common first step is a fat pad biopsy, where a small sample of abdominal fat is taken and stained with a dye called Congo red. Under a special microscope, amyloid deposits glow with a distinctive apple-green color. If the fat pad sample is negative but suspicion remains high, a biopsy of the affected organ may follow.
For heart involvement, echocardiography and cardiac MRI play central roles in detection, though a heart tissue biopsy remains the gold standard for definitive confirmation. Cardiac MRI is particularly useful because it can reveal characteristic patterns of amyloid infiltration in the heart muscle. Once amyloid is confirmed, additional testing determines which protein is involved, since the type dictates treatment. For ATTR amyloidosis, genetic testing identifies whether the hereditary or age-related form is responsible.
How Organ Involvement Affects Outlook
Survival with amyloidosis has improved substantially over the past four decades. For AL amyloidosis, median survival has risen from 1.4 years for people diagnosed in the 1980s to 4.6 years for those diagnosed between 2010 and 2019, driven largely by better therapies. Patients who are eligible for stem cell transplant have the best outcomes, with a median survival of nearly 9 years in the most recent era.
Heart involvement is the single biggest factor influencing prognosis. People with AL amyloidosis and no cardiac involvement have a median survival of 8.8 years with modern treatment, compared to 2.6 years for those whose hearts are affected. Even the most advanced cardiac cases have seen improvement, with median survival doubling from 6 months to about 12 months after newer treatment approaches became available around 2010.
For people over 70, who are more likely to have the wild-type ATTR form, outcomes have also improved, though more modestly. Early detection matters enormously across all types: the less organ damage that has occurred by the time treatment begins, the better the response tends to be.