Familial amyloid polyneuropathy (FAP) is a progressive neurodegenerative condition caused by a mutation in the transthyretin (TTR) gene. It is characterized by the buildup of abnormal TTR protein deposits (amyloids) in various parts of the body especially in the kidneys, peripheral nervous system, and heart. The buildup of amyloids, or amyloidosis, results in stiffness of the organs, thereby affecting their function and leading to the symptoms of FAP.
Cardiac involvement has been reported in about five to 23 percent of FAP cases. Older patients with FAP are at higher risk of developing cardiac complications, and 80 percent of FAP patients with cardiac involvement are men.
If left untreated, cardiac complications can cause heart failure within five to 15 years. Cardiac symptoms are usually preceded by peripheral neuropathy symptoms such as carpal tunnel syndrome (numbness, tingling, and pain in the arm and hands).
FAP-associated cardiac amyloidosis
The stiffening and thickening of heart muscles due to amyloidosis can cause cardiomyopathy or heart muscle disease, and hinder the heart’s ability to pump blood properly.
Most often, the first symptom of cardiac amyloidosis is arrhythmia or an irregular heartbeat. It may be present in patients for years before diagnosis.
Insufficient blood being pumped by the heart may cause shortness of breath, or dyspnea, which may be more evident upon physical exertion. Patients may tire quickly and experience weakness, fatigue, and fainting.
Some FAP patients may exhibit swelling in the legs due to water retention, a symptom of reduced heart function, which can lead to reduced blood flow that can cause angina or chest pain.
Diagnosis of cardiac involvement
Once cardiac involvement is suspected, imaging tests are used to visualize amyloid deposits, and determine heart health and function. Non-invasive exams include:
- Echocardiogram to assess the ability of the heart to pump blood
- Electrocardiogram (ECG or EKG) to measure the electric activity in heart muscles. Every time a heart beats, an electrical signal transfers through the muscle tissue. An ECG or EKG records this activity as a measure of heart function
- Cardiac magnetic resonance imaging to visualize the amyloid deposits in the heart
- Myocardial perfusion scintigraphy using a radioactive tracer to detect blood flow issues in the heart
In some instances, a myocardial biopsy may be recommended to confirm the diagnosis. This is an invasive procedure and, therefore, not frequently used.
Treatment of cardiac symptoms
Most therapeutic options currently available for FAP-associated cardiac amyloidosis are supportive in nature. For example, an irregular heart rhythm can be restored with cardioversion therapy or managed with antiarrhythmic medications. Pacemakers can help the heart beat so it can pump blood efficiently. In serious cases, doctors may recommend a heart transplantation in patients who have not responded to any other supportive treatments.
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