AL amyloidosis is a rare blood disorder in which abnormal bone marrow cells produce misshapen proteins that build up in organs, gradually damaging them. The “AL” stands for amyloid light chain, referring to the specific protein fragment that causes the problem. It most often affects the heart, kidneys, liver, and nerves, and it can be life-threatening if not caught early, particularly when the heart is involved.
How AL Amyloidosis Develops
The disease starts in the bone marrow, where a small group of plasma cells (the same type of white blood cell involved in multiple myeloma) becomes abnormal. These rogue plasma cells survive longer than they should because they ramp up genes that prevent normal cell death. As they accumulate, they churn out excessive amounts of immunoglobulin light chains, which are small protein fragments normally used to build antibodies.
In a healthy body, light chains fold into precise three-dimensional shapes and are cleared without trouble. In AL amyloidosis, the light chains are structurally unstable. Chemical modifications to the proteins, particularly changes that affect their solubility, push them toward misfolding. Instead of dissolving harmlessly in the bloodstream, they clump together into stiff, insoluble fibers called amyloid fibrils. These fibrils deposit in organ tissues, where they physically crowd out normal cells and also release toxic fragments that directly injure the tissue around them.
About 72% of cases involve lambda-type light chains, with the remaining 28% involving kappa-type. The type matters somewhat: kappa-based disease tends to affect the gastrointestinal tract and liver more often, while lambda-based disease leans toward kidney involvement.
Which Organs Are Affected
AL amyloidosis can deposit fibrils in nearly any organ, but four systems bear the brunt.
Heart. Amyloid deposits stiffen the heart muscle, reducing its ability to fill with blood between beats. Less blood gets pumped with each contraction, leading to shortness of breath, fatigue, and fluid retention. If the deposits disrupt the heart’s electrical system, irregular heart rhythms can develop. Cardiac involvement is the single biggest factor in determining how serious the disease is.
Kidneys. Amyloid damages the filtering system of the kidneys, often causing large amounts of protein to spill into the urine (a condition called nephrotic syndrome). Over time this can progress to kidney failure. Swelling in the legs and ankles is a common early sign.
Nerves. When amyloid infiltrates the peripheral nerves, it causes pain, numbness, or tingling in the hands and feet. Damage to the autonomic nerves, which control involuntary functions, can lead to alternating constipation and diarrhea, dizziness upon standing, or drops in blood pressure.
Liver. The liver can enlarge significantly as amyloid accumulates, sometimes causing a sense of fullness or discomfort in the upper abdomen.
Two physical signs are particularly distinctive. An enlarged tongue (macroglossia), sometimes with a rippled or scalloped edge from pressing against the teeth, is nearly unique to AL amyloidosis. Purplish bruising around the eyes, called periorbital purpura, results from amyloid weakening tiny blood vessels in the skin.
How It Is Diagnosed
Diagnosing AL amyloidosis requires four things: evidence of organ damage consistent with the disease, a tissue biopsy proving amyloid is present, confirmation of an abnormal plasma cell population, and identification of the amyloid as being made of light chains specifically.
The tissue biopsy is essential. A sample, often taken from abdominal fat or the affected organ itself, is stained with a dye called Congo red. Under polarized light, amyloid deposits produce a characteristic apple-green glow. But proving amyloid exists is not enough. Because the general condition of having abnormal plasma cells (called MGUS) is common in older adults, simply finding a monoclonal protein in someone’s blood does not confirm AL amyloidosis. The amyloid itself must be typed to confirm it is made of light chains and not another protein entirely.
Three methods can type amyloid. Immunohistochemistry is the most widely available. Immunoelectron microscopy offers better accuracy. Mass spectrometry is the gold standard, providing the highest sensitivity and specificity, and is particularly important in ambiguous cases.
Blood tests play a supporting role. A serum free light chain assay measures the levels of kappa and lambda light chains circulating in the blood. The ratio between them is abnormal in roughly 88% of AL amyloidosis patients, making it a useful screening and monitoring tool.
Staging and What It Means for Prognosis
Doctors stage AL amyloidosis based on how much stress the disease has placed on the heart and how much abnormal protein is circulating. The widely used Mayo staging system assigns one point for each of three findings: elevated levels of a heart-stress hormone (NT-proBNP at or above 1,800 pg/mL), a heart injury marker above a specific threshold (troponin T at or above 0.025 ng/mL), and a high difference between involved and uninvolved free light chains (18 mg/dL or greater). A score of zero is Stage I; a score of three is Stage IV.
The stage at diagnosis is the strongest predictor of survival. Patients with very advanced cardiac disease (Stage IV) have a median survival of roughly 4 to 8 months. Those with less severe heart involvement survive approximately 2 years on average, and patients diagnosed at Stage I often do considerably better, especially with effective treatment. This is why early detection, before significant heart damage has occurred, dramatically changes the outlook.
Treatment Approaches
Treatment targets the root cause: the abnormal plasma cells producing the toxic light chains. The goal is to reduce light chain production as quickly as possible so organs can stabilize or recover.
The current frontline regimen combines a targeted antibody therapy (daratumumab) with a three-drug chemotherapy backbone known as CyBorD. In the ANDROMEDA clinical trial, this combination produced a response in 96% of newly diagnosed patients, with 82% achieving a very good response or better. Most patients showed measurable improvement within the first month. This combination became the standard of care after demonstrating significantly deeper and faster responses than chemotherapy alone.
For patients who are physically strong enough, an autologous stem cell transplant remains an option. The procedure involves collecting your own stem cells, using high-dose chemotherapy to wipe out the diseased bone marrow, and then infusing the stem cells back to rebuild it. Transplant-eligible patients tend to have better long-term outcomes, though much of that advantage comes from the fact that only healthier patients qualify. Careful selection is critical: heart function, kidney function, age, and the number of organs involved all factor into eligibility. Case-control studies matching transplant recipients against similar patients who did not undergo transplant have shown a survival benefit, but the procedure carries real risks and is not appropriate for everyone.
Why Early Detection Matters
AL amyloidosis is often diagnosed late because its symptoms, such as fatigue, swelling, shortness of breath, and numbness, overlap with many common conditions. The median time from first symptoms to diagnosis can stretch months or even years. By the time the disease is recognized, significant organ damage may already exist.
Organ damage from amyloid is not always reversible. Kidney function can sometimes recover once the abnormal light chains are suppressed, and cardiac function improves in a subset of patients who achieve deep treatment responses. But organs that have been heavily infiltrated with amyloid may never fully return to normal. The difference between a Stage I and Stage IV diagnosis is not just a number on a chart. It can mean the difference between years of healthy life and months of declining function.