Workup of Amyloidosis

The diagnosis of amyloidosis and subsequent determination of amyloid subtype is critically important in the care of patients with amyloidosis. An analogy can be drawn to predictive marker testing in cancer care, since the subtype dictates treatment (and prognosis). 

How amyloid is detected and what methods are used in subtyping vary from laboratory to laboratory and evidence is lacking in terms of the most appropriate approach. New and coming treatments for systemic amyloidosis types underscore the importance of early detection and accurate subtyping and the timeliness of this guideline. 

Evidence supporting a recommendation is limited but seems to support the use of air-dried conventional smears, alcohol-fixed cytologic (cell block) preparations, and formalin-fixed-paraffin-embedded tissue blocks in the detection of amyloid in fat pad specimens.

The experience with and established validity of staining techniques in a given laboratory are important considerations in screening fat pad biopsies for amyloid.

Techniques yielding archived paraffin blocks (including cell block preparations) have the advantage of potential residual tissue for subtyping.

Evidence is lacking, but there are published articles suggesting that bilateral carpal tunnel syndrome (especially in patients without repetitive use history) and spontaneous biceps tendon rupture occur with higher frequency in systemic amyloidosis. Routine testing of carpal tunnel, lumbar stenosis, and biceps tendon specimens with special stains for amyloid is NOT recommended in this guideline, but having some index of suspicion in these cases is reasonable.

The treatment of systemic forms of amyloidosis depends on accurate subtyping, so fibril typing is essentially mandatory (see recommendation 4 and good practice statement 7) for these patients.

Localized amyloidosis may not require subtyping; although it may not be known at the time of first diagnosis whether it is localized of systemic. Fibril type determination may be necessary to determine whether it is localized or systemic.

Cases by case exceptions exist, such as when a patient is not a candidate or otherwise ineligible for any type of specific amyloid treatment. Even subtyping amyloid of autopsy tissue may be of benefit to surviving family members in cases of inherited amyloid types.

Recommendation 4 supports mass spectrometry as the optimal method for fibril typing ("pathologists should use mass spectrometry to identity the fibril protein type"), due to it’s superior accuracy, specificity, and open-ended methodology.

The guideline acknowledges that for renal biopsies, light chain typing by frozen section immunofluorescence "may often be successfully accomplished" but that "reflex to mass spectrometry-based proteomics should be performed in difficult or equivocal cases."

The strength of evidence was low for conditional recommendations in the guideline suggesting the need for more research in areas addressed by this effort. 

Further study, including large numbers of samples (>40), with control groups and comparison methods and clearly documented outcomes (results) are particularly needed in these areas:

• Fat pad biopsy testing methodologies
• Fat pad biopsy concordance with target organ biopsy
• Fat pad biopsy comparison to other surrogate biopsy types (rectal suction biopsy, salivary gland biopsy, etc.)
• Comparison of Congo red to other Amyloid stains (sensitivity/specificity)
• Novel amyloid fibril typing technologies (lower cost and faster turnaround time compared to mass spectrometry)