Screening Criteria for Amyloidosis Biopsy Testing during Carpal Tunnel Release in Community Hospitals: Evaluation and Application

Abstract

Background

Carpal tunnel syndrome (CTS) is a common disorder caused by median nerve compression. Current research has explored the relationship between CTS and cardiac amyloidosis, which can lead to poor health outcomes, highlighting the need for screening guidelines. Although recommendations exist for when to biopsy during carpal tunnel release (CTR), studies have primarily focused on urban or academic centers. This study evaluates these recommendations in a community hospital setting serving a predominantly rural population.

Materials and Methods

This retrospective study assessed risk factor based screening recommendations for intraoperative tenosynovial biopsy during open CTR. All procedures were performed by a single plastic surgeon. Positive Congo red staining samples were sent to the Mayo Clinic for confirmatory testing. Positive and negative amyloidosis cases were compared, with analyses stratified based on associated risk factors.

Results

The study included 105 patients (47.6% female) with a median age of 66.0 years old. Of these, 9.5% ( n  = 10) tested positive for amyloidosis. The median age of those who tested positive for amyloidosis was 81.5 years, compared with 65.0 years in those who tested negative. Of the 10 positive cases for amyloidosis, 7 patients had a history of chronic kidney disease (CKD), and 6 patients tested positive for the ATTR subtype.

Conclusion

With an overall amyloidosis positivity rate of 9.5%, this falls within range of previously reported positivity rates. Given the community hospital setting, ensuring follow-up is crucial, especially to determine if a positive result warrants amyloidosis treatment. Strong collaboration between hand surgeons and specialists is essential for coordinated local or tertiary care follow-up.

Introduction

Carpal tunnel syndrome (CTS) is among the most common upper extremity disorders in the United States (U.S.), with an annual incidence of 1 to 3 persons per 1,000 and a prevalence of 50 per 1,000. ¹ The pathophysiology of CTS is attributed to a combination of factors including compression, increased pressure, and traction on the median nerve. ¹ Although various causes such as anatomic variants, cysts, and rheumatological factors have been investigated, the exact etiology remains unclear in most cases. ^{1 2}

Numerous studies have shown an association between amyloidosis and CTS. ^{3 4 5} Sperry et al identified 10 of 98 patients as amyloid positive, and consequently proposed screening recommendations for when to biopsy during carpal tunnel release (CTR). ⁵ Subsequently, another study found a 22.5% amyloidosis positivity rate among patients meeting these proposed screening criteria during CTR. ⁶ Other studies showed similar associations, with one finding a 21.2% positivity rate in men over 70 years old with CTS. ⁷ Another study identified positive Congo red stain results in 29% of patients (54 of 185 individuals) undergoing tenosynovial biopsy, with male sex, atrial fibrillation, and spinal stenosis being associated conditions. ⁸ These findings underscore the importance of systematic screening for amyloidosis in select patient populations with CTS.

Despite advancements in identifying associated risk factors for amyloidosis, notable challenges in applicability and coordination of care remain. Previous research revealed 31.8% of patients with amyloidosis consulted with more than five physicians before receiving their diagnosis, highlighting the complexity of recognizing the condition. ⁹ Given 90% of the U.S. population receives their care in community hospitals, access to surgeons and physicians who are knowledgeable about this disease is critical to improving early detection and identifying who needs treatment. ⁹ In the context of CTS and amyloidosis, one study found that among individuals with CTS, those with bilateral involvement were 11 times more likely to have cardiac amyloidosis (CA). ^{10 11} Regarding CA, autopsy studies reported myocardial amyloid deposits in 20 to 25% of individuals over the age of 80 years. ^{9 12} If progression to CA occurs, it is associated with a poor prognosis and average survival ranging from 3.6 to 5.8 years. ^{9 13} As the aging population continues to grow, it is essential to develop systems that not only facilitate early recognition and appropriate screening, but also efficient mechanisms for follow-up and timely treatment.

The established association between CTS and amyloidosis emphasizes the importance of early detection of amyloid deposits. ⁵ With the ability to detect amyloid in tenosynovial biopsies obtained during CTR, it could facilitate proactive treatment of amyloid-related diseases. Proposed screening recommendations for biopsy have been based on age, sex, bilateral carpal tunnel symptoms or prior release surgery, spinal stenosis, biceps tendon rupture, atrial fibrillation or flutter, pacemaker presence, congestive heart failure, and/or family history of ATTR ( Table 1 ). ^{5 14} These criteria are two-tiered, serving as a guide for when to biopsy patients during CTR ( Table 1 ). This study aimed to evaluate previously described screening guidelines for tenosynovial biopsy during CTR in a community hospital setting serving a predominantly rural population.

Table 1. Recommendations for biopsy to test for amyloidosis during carpal tunnel release surgery ⁵ .

Tier I criteria	Tier II criteria
Male age ≥50 years old	Spinal stenosis
Female age ≥60 years old	Biceps tendon rupture
Bilateral carpal tunnel symptoms or prior release surgery	Atrial fibrillation or flutter
	Pacemaker
	Congestive heart failure
	Family history of ATTR amyloidosis

Note: Perform intraoperative tenosynovial biopsy if one of the following conditions are met:

Scoring Option 1: Two characteristics from Tier I.

Scoring Option 2: One characteristic from Tier I plus any one characteristic from Tier II.

Materials and Methods

The open CTR surgery and biopsy were all performed by one plastic surgeon at one community hospital. Patients underwent tenosynovial biopsy at the time of CTR if they met Tier I or Tier II criteria as described by Sperry et al ( Table 1 ). ⁵ Tier I criteria include males age ≥50 years old, females ≥60 years old, or presence of bilateral carpal tunnel symptoms or prior release surgery. Tier II criteria include those with history of spinal stenosis, biceps tendon rupture, atrial fibrillation or atrial flutter, pacemaker placement, congestive heart failure, or family history of ATTR amyloidosis. Patients need two characteristics from Tier I or one from Tier I and one from Tier II to meet criteria for biopsy at the time of CTR. Patients presenting to the clinic with CTS symptoms including numbness, tingling, burning, or prickling sensations in the median nerve distribution, sensitivity to cold or heat, as well as worsening symptoms at night were triaged according to the algorithm in Table 1 . If they met the criteria either by scoring option one or scoring option two, it was recommended they underwent a tenosynovial biopsy at the time of their CTR.

After obtaining approval from the local healthcare system's institutional review board to conduct this retrospective cohort study, we identified all patients who underwent tenosynovial tissue biopsy during CTR surgery at a community hospital from March 1, 2022 through October 31, 2023. The study design was created based on the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines. ¹⁵ After obtaining our patient list we created a unique identification code for all patients. All identifying information was removed and stored on an offline encrypted database.

Data collected from patient charts included demographic information, such as age, race, BMI, and sex. History of chronic disease, including cardiovascular, kidney, endocrine-related, and musculoskeletal diseases were reviewed with the patient by the surgeon and extracted from the electronic medical record (EMR). Notable musculoskeletal disease information collected included history of biceps tendon rupture, CTS, spinal stenosis, and trigger digit. A binary determination of disease history was made based upon diagnosis history in the patients' medical records. Corresponding laboratory values reflecting measurements of these bodily systems were also extracted. Additional data were extracted in accordance with the risk factors proposed by Sperry et al. ⁵ Two sets of biopsy sample results were then collected for amyloidosis status, one set being a preliminary set of results from our local healthcare system that observed for apple-green birefringence and, if positive, a second set sent to the Mayo Clinic for confirmatory staining and mass spectrometry. The amyloidosis test results used in this study were from the mass spectrometry results obtained from the Mayo Clinic.

Results were considered statistically significant when p  < 0.05. For variables with a non-normal distribution, median and interquartile range (IQR) were reported. Due to the non-normal distribution of the continuous variables, the Mann-Whitney U test was used to investigate differences between the two groups. For categorical variables, Pearson's chi-square tests were used to investigate differences between the two groups. A post hoc power analysis was conducted for both tests. The results indicated that the Pearson's chi-square test showed sufficient power, while the Mann-Whitney U test was below the acceptable threshold of 80% power. Therefore, for categorical variables, the descriptive statistics and associated p -values from significance testing are presented. For continuous variables, the study reports descriptive statistics. To handle missing data for certain laboratory values, due to lack of record in available charts, the series mean imputation method was used for variables with less than 20% missing values. Alternatively, variables with more than 20% missing values were excluded from the statistical significance testing to maintain the reliability of the results.

Results

A total of 105 patients (47.6% female, n  = 50) with a median age of 66.0 years (IQR of 61.0–76.0 years old) underwent CTR with concomitant tenosynovial biopsy ( Table 2 ). Of these patients, 9.5% ( n  = 10) cases tested positive for amyloidosis confirmed by mass spectrometry after Congo red staining ( Table 2 ). Of the 10 positive cases 6 were confirmed to have the ATTR subtype of amyloidosis ( Table 3 ).

Table 2. Descriptive statistics between amyloidosis and non-amyloidosis groups.

Clinical values	Total ( n  = 105)	Non-amyloidosis ( n  = 95)	Amyloidosis ( n  = 10)	p -value
Age (years)	66.0 (61.0–76.0)	65.0 (60.0–75.0)	81.5 (65.8–84.3)	–
Gender (female)	50 (47.6%)	46 (48.4%)	4 (40.0%)	0.745
Race				1.000
White	93 (90.3%)	84 (90.3%)	9 (90.0%)
Non-White	10 (9.7%)	9 (9.7%)	1 (10.0%)
BMI (kg/m 2 )	32.1 (28.7–36.0)	32.1 (28.7–36.0)	31.9 (28.1–34.2)	–
CKD	31 (29.5%)	24 (25.3%)	7 (70.0%)	0.007
Biceps tendon rupture	7 (6.7%)	7 (7.4%)	0 (0%)	1.000
Diabetes	48 (45.7%)	39 (41.1%)	9 (90.0%)	0.005
Hypertension	88 (83.8%)	78 (82.1%)	10 (100%)	0.360
Heart failure	19 (18.1%)	14 (14.7%)	5 (50.0%)	0.016
Atrial fibrillation	21 (20.0%)	16 (16.8%)	5 (50.0%)	0.026
Atrial flutter	9 (8.6%)	8 (8.4%)	1 (10.0%)	1.000
Pacemaker placement	7 (9.3%)	6 (9.1%)	1 (11.1%)	1.000
Spinal stenosis	43 (41.0%)	38 (40.0%)	5 (50.0%)	0.737
Thyroid disease	19 (18.1%)	15 (15.8%)	4 (40.0%)	0.079
Trigger digit	37 (35.2%)	33 (34.7%)	4 (40.0%)	0.739
Trigger digit release categories				0.919
History of trigger digit release	22 (21.2%)	20 (21.3%)	2 (20.0%)
Trigger digit, no history of release	15 (14.4%)	13 (13.8%)	2 (20.0%)
No trigger digit, no release	67 (64.4%)	61 (64.9%)	6 (60.0%)
Carpal tunnel syndrome	105 (100%)	95 (100%)	10 (100%)	–
Side of carpel tunnel syndrome				0.233
Right	30 (28.6%)	28 (29.5%)	2 (20.0%)
Left	27 (25.7%)	26 (27.4%	1 (10.0%)
Bilateral	48 (45.7%)	41 (43.2%)	7 (70.0%)	0.180

Abbreviations: CKD, chronic kidney disease; kg/m ² , kilograms/meters squared; LVEF, left ventricular ejection fraction.

Note: All values presented as n (%) or median (interquartile range). A p -value < 0.05 was considered to be statistically significant. The table reports associated two-sided p -value from Pearson's chi-square test. For variables in which Pearson's chi-square test assumptions are violated due to greater than 20% of cells having a frequency of less than 5, Fisher's exact test statistic or likelihood ratio test and associated p -values are reported.

Table 3. Characteristics of patients with ATTR subtype.

Patient	Amyloid type	Age	Sex	Race	CKD	Diabetes	HTN	Hx of HF	Hx of AF	Atrial flutter	Hx of SS	Family Hx of ATTR	Trigger digit	Thyroid disease	Side of carpal tunnel
#1	ATTR	62	Male	White	No	Type 2	Yes	No	No	No	Yes	No	Yes	No	Bilateral
#2	ATTR	78	Male	White	Yes	Type 2	Yes	No	No	No	Yes	No	Yes	Yes	Right
#3	ATTR	81	Male	White	No	Type 2	Yes	No	No	No	No	No	No	No	Bilateral
#4	ATTR	82	Male	White	Yes	Type 2	Yes	Yes	Yes	No	No	No	No	No	Bilateral
#5	ATTR	85	Female	White	Yes	Type 2	Yes	Yes	Yes	Yes	Yes	No	No	No	Bilateral
#6	ATTR	88	Female	White	Yes	Type 2	Yes	Yes	Yes	No	No	No	No	No	Bilateral

Abbreviations: AF, atrial fibrillation; CKD, chronic kidney disease; HF, heart failure; HTN, hypertension; Hx, history; SS, spinal stenosis.

Descriptive statistics comparing groups with and without amyloidosis are given in Table 2 . Patients in the amyloidosis group were older than those in the non-amyloidosis group, with median ages of 81.5 years (IQR: 65.8–84.3) and 65.0 years (IQR: 60.0–75.0), respectively ( Table 2 ). Of those who tested positive for amyloidosis, 7 of 10 patients (70%) had chronic kidney disease (CKD), compared with 24 patients (25.3%) in the non-amyloidosis group ( p  < 0.05) ( Table 2 ). Additionally, diabetes was identified in 9 of the 10 patients in the amyloidosis group (90%), compared with 39 patients (41.1%) in the non-amyloidosis group, with a p -value of <0.05 ( Table 2 ). In the amyloidosis group, 5 (50%) had a history of heart failure, compared with 14 (14.7%) in the non-amyloidosis group, with a p -value of <0.05 ( Table 2 ). In the amyloidosis group, 5 (50%) had a history of atrial fibrillation versus 16 (16.8%) in the non-amyloidosis group, with a p -value <0.05 ( Table 2 ). Lastly, 7 (70%) of positive amyloidosis cases had bilateral CTS while 41 (43.2%) of negative amyloidosis cases had bilateral CTS. Laboratory values comparing both the groups are shown in Table 4 . Of the 10 patients in this study 1 is known to have started treatment for amyloidosis at a tertiary care center.

Table 4. Laboratory values for amyloidosis and non-amyloidosis groups.

Laboratory values	Total ( n  = 105)	Non-amyloidosis ( n  = 95)	Amyloidosis ( n  = 10)
HgbA1c (%)	6.4 (5.9–6.5)	6.1 (5.5–6.7)	6.5 (6.0–7.0)
BUN (mg/dL)	17.0 (14.0–21.5)	17.0 (14.0–20.0)	18.8 (16.0–29.0)
Creatinine	0.9 (0.8–1.2)	0.9 (0.8–1.1)	1.1 (0.9–1.4)
Microalbumin/ Creatinine ratio	14.0 (9.0–40.5)	21.5 (9.8–68.5)	10.5 (5.3–12.8)
GFR ≥ 60 (mL/min)	75 (79.8%)	71 (82.6%)	4 (50.0%)
AST (U/L)	24.0 (19.0–29.0)	24.0 (19.0–29.0)	20.5 (18.8–25.6)
ALT (U/L)	23.0 (16.0–30.0)	24.0 (17.0–29.0)	22.0 (20.5–25.2)
Alkaline phosphatase (IU/L)	84.0 (68.0–96.5)	85.0 (67.0–102.0)	83.5 (77.8–87.6)

Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; GFR, glomerular filtration rate; HgbA1c, hemoglobin A1c; IU/L, international units/L; mg/dL, milligrams/deciliter; mL/min, milliliters/minute; U/L, units/liter.

Note: All values presented as n (%) or median (interquartile range).

Tables 3 and 5 show characteristics of the six ATTR-positive individuals. All six patients were at least 60 years old, with four older than 80 years. Four of the six individuals were male, and all were categorized as having a white ethnicity. Four of the six individuals had a history of CKD, and all six individuals had a history of type 2 diabetes, hypertension, and CTS. Half of the individuals had a history of atrial fibrillation, heart failure, and spinal stenosis, while only two had a history of trigger digit and one had a history of atrial flutter.

Table 5. Laboratory results for patients with ATTR subtype.

Patient	Amyloid type	HgbA1c (%)	BUN (mg/dL)	Creatinine (mg/dL)	Microalbumin/ Creatinine ratio	GFR (mL/min)	AST (U/L)	ALT (U/L)	Alkaline phosphatase (IU/L)
#1	ATTR	6.70	18.00	1.10	12	≥60	29	30	65
#2	ATTR	5.80	43.00	1.80	–	–	–	–	–
#3	ATTR	5.80	16.00	0.80	7	≥60	20	23	83
#4	ATTR	7.10	35.00	1.40	0	<60	18	9	101
#5	ATTR	7.00	15.00	0.93	12	≥60	33	21	87
#6	ATTR	8.00	23.00	1.20	9	<60	19	21	84

Abbreviations: ALT, alanine aminotransferase; AST, aspartate aminotransferase; BUN, blood urea nitrogen; GFR, glomerular filtration rate; HgbA1c, hemoglobin A1c; IU/L, international units/L; mg/dL, milligrams/deciliter; mL/min, milliliters/minute; U/L, units/liter.

Discussion

This study evaluated the applicability of previously described screening recommendations for amyloidosis biopsy during CTR in a community hospital setting. Our results confirm that the recommendations proposed by Sperry et al are reproducible in community-level practices. Among 105 patients, 9.5% ( n  = 10) tested positive for amyloidosis, a rate consistent with Sperry et al (10.2%), but lower than Gannon et al (22.5%) and DiBenedetto et al (29%). ^{5 6 8} These variations may reflect differences in patient demographics or regional risk factor prevalence.

All patients underwent CTR with tenosynovial tissue biopsy, limiting assessment of amyloidosis risk specifically tied to the procedure. Prior research indicates bilateral CTS as a red flag symptom for amyloidosis. ^{5 8} Although our sample size limited statistical associations, 70% of amyloidosis-positive patients had bilateral CTS. Additionally, 9 out of 10 amyloid-positive cases had confirmed bilateral CTS on electromyogram, reinforcing its importance as a screening criterion.

Patients with amyloidosis were older (median age 81.5 versus 65.0 years in the non-amyloidosis group). Due to a post hoc power analysis indicating that the Mann-Whitney U test had less than 80% power, the sample was considered underpowered. As a result, p -values for continuous variables were omitted, and conclusions were drawn based on descriptive statistics. Of the amyloidosis-positive cases, 60% (6 of 10) were male, with 4 of those 6 being ATTR positive. This is consistent with existing evidence that male sex and age ≥50 years are risk factors for amyloidosis. ^{5 6 8 16 17}

Our analysis also found a significant bivariate association between CKD and positive amyloidosis results, with four out of six ATTR-positive individuals also having CKD. Given the overlap of CKD with both amyloidosis and the comorbidities assessed with the screening recommendations, further assessment may be needed within the context of the screening criteria. ^{18 19} Although chronic renal failure has been identified as a comorbidity for diagnosing cardiac amyloidosis after CTR, CKD history and severity of CKD have not yet been considered in CTR biopsy screening. ¹⁹ As a result, further investigation may be warranted to delineate if history of CKD and corresponding stage have a true association or is an incidental finding, and whether hand surgeons should consider it in their screening criteria.

Detection of amyloidosis through CTR biopsy is clinically valuable due to opportunity for earlier intervention. Amyloid deposits are frequently present in carpal tunnel tissues, with positivity rates of 10 to 20% during CTR. ^{5 19 20} However, progression to cardiac amyloidosis greatly varies in these patients with a positive CTR biopsy. ^{5 19} Overall, the ability to detect deposition early allows for timely intervention with the goal of limiting poor outcomes associated with cardiac amyloidosis.

In addition to clinical implications, cost-effectiveness of performing biopsies during CTR must also be considered. Although there are increased procedural costs to perform biopsies, early detection can help prevent downstream costs associated with more resource-intensive measures for late-stage diagnosis and treatment. For heart failure–related hospital stays, average costs are $14,600 with a mean stay of 7.07 days. ⁹ By integrating biopsies into CTRs, already scheduled surgeries can be leveraged to minimize costs while facilitating earlier diagnosis and intervention.

Alternative screening approaches, including abdominal fat pad aspirates, have been proposed as less invasive and potentially cost-effective options for amyloidosis detection. A recent study has proposed when to undertake biopsy, either during a CTR or via obtaining an abdominal fat pad aspirate. ²⁰ Focus was on multidisciplinary approaches involving hand surgeons and other providers for the type of biopsy to perform. ^{20 21} Furthermore, new screening measures covered by insurance are also emerging, such as buccal swabs and blood tests. ^{22 23 24} For patients undergoing CTR, incorporating a biopsy during surgery remains a practical and efficient approach for identifying amyloidosis. The choice of screening approach ultimately depends on the clinical context, available resources, and a healthcare system's capacity to follow up on positive findings or ability to provide a specialist referral.

Once positive biopsy results are obtained, robust coordination is essential to ensure appropriate follow-up for these patients. It has been proposed to create cardiac amyloidosis centers in community hospitals via more training and resource allocation to improve access to care and limit travel distances. ^{9 21} At our community hospital, patients were initially referred to tertiary centers, but this has progressively transitioned to local management with neurologists and cardiologists. Although hematologists usually initiate systemic amyloidosis treatment, at our hospital, it is one of the neurologists who has taken on that role. If a patient is confirmed to have tested positive for amyloidosis, the patient is scheduled for follow-up with the plastic surgeon, and referred to a cardiologist and a neurologist. By ensuring this appropriate follow-up, the surgeon follows the postoperative course of the patient and can monitor for further symptoms; the cardiologist assesses for any possible cardiac manifestations through diagnostic testing; and the neurologist is able to evaluate for possible initiation of amyloidosis treatment and again assess for any additional new numbness or tingling. In particular, for patients who have the ATTR subtype, it is extremely important for them to undergo cardiology evaluation for potential cardiac involvement. It is also important to be mindful that these patients may have other systemic manifestations affecting other organs such as the kidneys or the eyes, necessitating further specialty evaluation. As a result of implementing these strategies, community hospitals can optimize amyloidosis screening during CTR with the goal of improving both clinical and economic outcomes for patients.

Treatment options and associated costs must also be considered. Of the 10 individuals tested positive for amyloidosis 1 is being treated with Diflunisal, a non-steroidal anti-inflammatory used off-label. ²⁵ One current treatment for cardiac amyloidosis, tafamidis, costs upwards of $250,000 per year, requiring a 92.6% reduction needed for cost-effectiveness. ^{19 26} Vutrisiran, recently approved for hereditary transthyretin amyloidosis with polyneuropathy, can exceed $400,000 annually. ²⁷ Therefore, while studying amyloidosis is scientifically important due to its potential for causing cardiac amyloidosis, knowing the value in terms of quality-adjusted life years must be evaluated.

This study has limitations inherent to its retrospective design and small sample size, which reduces statistical power and complicates undertaking multivariate analysis. Furthermore, the low number of positive amyloidosis cases introduces additional statistical limitations that warrant cautious interpretation of the results. This also increases potential for type II errors and over-interpretation of bivariate associations. Despite the limited number of positive cases, the Pearson's chi-square test provided adequate power from post-hoc power analysis to detect significant differences. However, sample size and an imbalanced dataset limit statistical analysis to only bivariate associations. The interconnectedness and high prevalence of hypertension, diabetes, and CKD in the U.S. may influence our findings. Additionally, data extracted from EMRs may lack completeness. Biopsy samples negative on Congo red staining were not subjected to mass spectrometry, potentially leading to false negatives. The protocol of only conducting mass spectrometry on Congo red positive samples is a decision made by Mayo Clinic Laboratories, and outside of the research team's purview. However, it does limit the ability to closely analyze each sample, which could lead to a lower positivity rate. Also, user-dependent Congo red staining likely contributed to our lower positivity rate compared with other studies. Notably, our center reported almost double the positivity rate compared with the Mayo Clinic on the same samples. Although we observed a bivariate association between CKD and amyloid deposition, future research should investigate this relationship while accounting for confounding factors using a larger sample size and developing multivariate models. As such, the findings from this sample should be interpreted as exploratory and may not be generalizable to broader populations.

In summary, our findings underscore the feasibility and replicability of implementing amyloidosis screening biopsies during CTR in the community hospital setting, with the potential to both identify patients with amyloidosis early and reduce the healthcare burden associated with advanced disease. Further studies are needed to refine cost-effectiveness models, compare alternative screening methods, and assess the long-term impact on patient outcomes.