Recognizing ATTR Cardiomyopathy and Its Non-Biopsy Diagnosis

Key Takeaways:

• ATTR-CM often hides within heart failure with preserved ejection fraction. The highest-yield red flags – increased wall thickness with a discordantly low QRS voltage, and bilateral carpal tunnel syndrome – should prompt a dedicated workup.
• Grade 2 or grade 3 cardiac uptake on bone scintigraphy, combined with a mandatory monoclonal-protein exclusion, can establish ATTR-CM without endomyocardial biopsy.
• TTR genotyping after diagnosis separates wild-type from hereditary disease; wild-type is the more common cardiac form, and a hereditary result triggers family screening.

Transthyretin amyloid cardiomyopathy (ATTR-CM) is an increasingly recognized cause of heart failure, particularly heart failure with preserved ejection fraction (HFpEF), and the arrival of disease-modifying therapy has made timely recognition consequential.¹

The condition reaches clinicians from 2 directions: the cardiologist evaluating unexplained left ventricular wall thickening, and the neurologist or hand surgeon who encounters bilateral carpal tunnel syndrome or a hereditary mixed phenotype years before cardiac symptoms appear. Now that a validated noninvasive pathway exists, the key is to recognize the phenotype and reach an ATTR cardiomyopathy diagnosis without resorting to an endomyocardial biopsy.¹

Cardiac and extracardiac red flags

Several features should raise suspicion when they cluster. On the cardiac side, the consensus highlights increased left ventricular wall thickness with symptoms of heart failure, a QRS voltage that is discordantly low for the degree of wall thickening, conduction system disease, atrial fibrillation, a pseudoinfarct pattern on electrocardiogram (ECG), and intolerance to vasodilating antihypertensive medications.¹

Low QRS voltage – classically discordant with the degree of wall thickening – is present in only a minority of patients, so its absence does not exclude the diagnosis.¹

Extracardiac clues often precede the cardiac presentation by years: bilateral carpal tunnel syndrome, lumbar or cervical spinal stenosis, and spontaneous biceps tendon rupture. The last 2 noted as relatively specific to ATTR – along with peripheral neuropathy, autonomic dysfunction, and orthostatic hypotension.¹

Confirming without biopsy

Once amyloidosis is suspected on history, examination, ECG, and echocardiography, the pathway proceeds to radionuclide bone scintigraphy using technetium-99m-labeled tracers – pyrophosphate (PYP), 3,3-diphosphono-1,2-propanodicarboxylic acid (DPD), or hydroxymethylene diphosphonate (HMDP).^1,2

In a landmark multicenter validation study, any positive cardiac uptake greater than 99 percent was sensitive for cardiac ATTR, with a specificity of 86 percent. The specificity is imperfect chiefly because light-chain amyloidosis (AL) can also take up tracer.²

Adding the monoclonal-protein step is what improves specificity: grade 2 or grade 3 cardiac uptake combined with the absence of a monoclonal protein reached 100 percent specificity and positive predictive value for ATTR-CM, establishing the diagnosis noninvasively.²

A negative or equivocal scan does not by itself exclude ATTR-CM – some hereditary variants, such as Phe64Leu, can produce false-negative scans – so when clinical suspicion remains high, or when scintigraphy is unavailable, endomyocardial biopsy with amyloid typing remains the gold standard.¹

Excluding AL amyloidosis

Scintigraphy alone is not enough. Monoclonal-protein screening is mandatory and must combine serum immunofixation electrophoresis (IFE), urine IFE, and a serum free light chain assay – no single test is sufficient.²

The exclusion matters because AL amyloidosis is a different disease, is treated differently, and can be rapidly fatal if missed. A monoclonal protein and ATTR can also coexist – in roughly 10 to 40 percent of patients with ATTR-CM across series, and in 107 of 562 patients (19 percent) in the scintigraphy validation cohort.^1,2

A positive scan in a patient who has a monoclonal protein therefore does not confirm ATTR – it mandates histologic or proteomic typing to distinguish ATTR from AL.²

Genotyping to assign subtype

A confirmed ATTR-CM diagnosis is not complete until TTR gene sequencing assigns the subtype. Genotyping distinguishes wild-type disease (ATTRwt-CM), the more common cardiac form, from hereditary disease (ATTRv-CM).^1,2

The distinction is not academic: hereditary disease is autosomal dominant, so identifying a pathogenic variant opens genetic counseling and cascade screening of at-risk relatives, and the hereditary form is where a mixed cardiac-and-neurologic phenotype is most likely. For the neurologist or hand surgeon who first meets these patients, recognizing the extracardiac pattern and referring for cardiac evaluation is the highest-value step toward a diagnosis that is now actionable.¹