Could the MAC Score be a Game-Changer in Assessing Patients with CLTI?
7. October 2021
Jeff Hall, Senior Contributing Editor

In a recently published study, researchers found that the medial arterial calcification (MAC) score, which can be obtained from plain foot radiographs, may be a highly predictive risk factor for major amputation in patients with chronic limb-threatening ischemia (CLTI).1

In the retrospective study, published online by the Journal of Vascular Surgery, Liu and co-authors assessed 250 patients with CLTI who were treated with infrainguinal revascularization over an eight and a half-year time frame.1 After assessing plain foot radiographs for these patients, a blinded reviewer assigned a MAC score ranging from 0 to 5, based on the total amount of calcification seen in different arterial segments in the foot, according to the study, which was presented at the 35th Western Vascular Society Annual Meeting last month in Santa Monica, Calif. The authors found that the MAC score was a “strong independent predictor of major amputation in patients with CLTI.”1

“The results of this study have a very powerful message regarding calcified arteries,” suggests Alexander Reyzelman, DPM, FACFAS, a co-author of the study and Co-Director of the University of California-San Francisco (UCSF) Center for Limb Preservation. “We now are able to use this data to help in the decision-making process with patients who have CLTI.”

“Calcification of peripheral arteries has long been understood to be a risk factor for cardiovascular events, adverse limb occurrences and a nemesis for procedural interventions and technical outcomes,” notes Shant Vartanian, MD, a co-author of the study and a Professor of Surgery within the Division of Vascular and Endovascular Surgery at the University of California-San Francisco (UCSF). “What is novel about the MAC score is the first application to the below-ankle circulation, which is becoming a progressively bigger problem in our increasingly diabetic society.”

Dr. Vartanian credits Roberto Ferraresi, MD for the development and initial online publication about the MAC score in 2020.2 While Dr. Vartanian points out that the MAC score has only been the subject of retrospective study thus far in a narrow population of patients, he says early investigations suggest the MAC score has tremendous power in predicting limb-specific events.

“As follow-up publications are produced and as the MAC score is presented at meetings, I suspect it will disseminate quickly, given its ease of use and prognostic power,” maintains Dr. Vartanian.

Medial arterial calcinosis is very common in patients with diabetes and renal disease, and it is well-established that ankle-brachial indexes (ABIs) can be falsely elevated in these populations as a result, according to Dr. Reyzelman, a Professor within the Department of Medicine at the California School of Podiatric Medicine at Samuel Merritt University. However, in patients with peripheral arterial disease (PAD) who do not have diabetes, Dr. Reyzelman says there is a perception that ABIs are reliable because these patients are less likely to have medial calcinosis.

“The truth is that even patients with PAD can have other comorbidities that may lead to medial calcinosis,” points out Dr. Reyzelman. “The only way to find out if someone has medial calcinosis is to have an X-ray of the foot taken.”

Drs. Reyzelman and Vartanian praise the simplicity and accessibility of the MAC score technique, noting that plain X-ray films are a routine part of assessing foot wounds in patients with diabetes. Using a two-view X-ray of the foot, Dr. Vartanian says one can calculate the MAC score by assigning one point each for “tram track”-like calcifications in five arterial segments: the dorsalis pedis, plantar, metatarsal, hallux digital and non-hallux digital arteries. The MAC score ranges from 0-5 with 0-1 being mild, 2-3 being moderate and 4-5 being severe, according to Dr. Vartanian.

“The MAC score takes only a few seconds to calculate, and early work has shown that the method is highly reproducible between providers,” notes Dr. Vartanian.

The study authors also found that in subsets of patients with WIfI stages 3 and 4, and patients with diabetes, use of the MAC score allowed for increased stratification of major amputation risk.1

“The Society for Vascular Surgery’s WIfI classification is already very robust at predicting which diabetic limbs are at highest risk, and the MAC score was able to add significant resolution within each WIfI strata, particularly those in the highest risk group,” points out Dr. Vartanian.1,3 “It speaks to one potential application of the score: helping sort out which stage IV limbs can be managed successfully with standard interventions and which patients need intensive therapy to achieve success.”

“The ability to prognosticate the threat of limb loss is critically important in amputation prevention,” emphasizes Dr. Reyzelman. “The MAC score can be used in addition to the WIfI classification and complement non-invasive tests in better assessing limb threat.”

Dr. Vartanian acknowledges there is still a lot to learn about the MAC score and its utility outside of patients with CLTI. He says further validation of the MAC score is necessary and he believes that will come with time and careful prospective observational studies. However, when he encounters a patient with a MAC score of 4 or 5 in his practice, Dr. Vartanian notes the emerging research on the MAC score does impact how he treats such a patient.

“It sets off an alarm in my mind that this patient is at high risk for a poor outcome and there is no margin of error over the course of treatment,” acknowledges Dr. Vartanian. “(A higher MAC score) tends to result in more intensive interventions and follow-up than what we would expect with standard practice.”

References

1. Liu IH, Wu B, Krepkiy V, et al. Pedal arterial calcification score is associated with the risk of major amputation in chronic limb-threatening ischemia. J Vasc Surg. 2021 Sep 3;S0741-5214(21)01978-9. doi: 10.1016/j.jvs.2021.07.235. Online ahead of print.

2. Ferraresi R, Ucci A, Pizzuto A, et al. A novel scoring system for small artery disease and medial arterial calcification is strongly associated with major adverse limb events in patients with chronic limb-threatening ischemia. J Endovasc Ther. 2021;28(2):194-207. doi: 10.1177/1526602820966309. Epub 2020 Oct 15.

3. Zhan LX, Branco BC, Armstrong DG, Mills JL Sr. The Society of Vascular Surgery lower extremity threatened limb classification system based on wound, ischemia, and foot infection (WIfI) correlates with risk of major amputation and time to wound healing. J Vasc Surg. 2015;61(4):939-44.

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