Novel screening for transthyretin amyloidosis by using fat ultrasonography
The systemic amyloidosis hereditary transthyretin (TTR) amyloidosis, or TTR‐related familial amyloid polyneuropathy (FAP), is a common cause of hereditary polyneuropathy worldwide. More than 130 point mutations and a deletion in the TTR gene have been reported as causes of this amyloidosis, with amyloidogenic transthyretin (ATTR) V30M (p.V50M) being the most common mutation and affecting systemic organs and tissues, including peripheral nerves, autonomic nervous system, heart, gastrointestinal system, kidneys, eyes, and skin.1 Typical patients with early onset ATTR V30M amyloidosis in endemic foci have strong family histories, severe autonomic dysfunction, and surface sensory disturbances associated with a loss of small‐diameter nerve fibers.1 Patients with late onset disease from nonendemic areas have no or unclear family histories and noncharacteristic neuropathic patterns with nonspecific nerve loss in both large and small fibers, and they sometimes have disease that mimics other types of neuropathy, such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), especially at presentation.3 The misdiagnosis and delay in diagnosis leads to lost opportunities for treatments such as liver transplantation, use of TTR stabilizers, and gene silencing.7 Ruling out hereditary TTR amyloidosis in patients with neuropathy with undetermined etiology is thus important, and TTR gene tests and histopathological analyses of biopsy samples from affected organs and tissues are needed. In systemic amyloidosis, subcutaneous fat is a common site of amyloid deposition, and abdominal fat pad fine‐needle aspiration has been useful for diagnosis of the different systemic amyloidoses.8 Sensitivity of the method ranges between 52% and 88%,9 and this variation may be related to small sample sizes and limited areas of aspirated fat tissue. Fat smears on glass slides, Congo red staining, and polarized light microscopy are established methods and are used by major medical centers, particularly in endemic areas. A more general noninvasive screening method may yield better diagnoses. Here, we present a novel noninvasive, simple screening method that utilizes conventional ultrasound equipment to detect subcutaneous amyloid deposition in abdominal fat.