Electromyography in Anticoagulated Patients
March 1, 2012 3 minutes read
Electromyography in Anticoagulated Patients
Abstract & Commentary
By Michael Rubin, MD, Professor of Clinical Neurology, Weill Cornell Medical College. Dr. Rubin reports no financial relationships relevant to this field of study.
Synopsis: Needle EMG is safe in patients who are taking therapeutic doses of antiplatelet or anticoagulant medications.
Source: Boon AJ, et al. Hematoma risk after needle electromyography. Muscle Nerve 2012;45:9-12.
Patients on antiplatelet agents or anticoagulants often require needle electromyography (EMG), and the risk of hematoma formation and uncontrolled bleeding is often raised. Many EMG laboratories avoid studying such patients.1 No evidence-based guidelines exist, although it is generally recommended that EMG not be performed if the platelet count is lower than 50,000/mm3, the internationalized normalized ratio (INR) is greater than 3, or the partial thromboplastin time (PTT) is greater than twice the control value.2 What are the evidence-based facts? Is there an increased risk of hematoma formation? Should deep muscles be avoided?
In this Mayo Clinic-based, prospective, case-controlled study, 205 patients referred for EMG were divided into three groups, those on (1) warfarin, (2) clopidogrel or aspirin or both, and (3) neither of the above (who served as controls). In each group, at least 100 muscles, arbitrarily defined as "muscles-of-interest," were studied, including the cervical, thoracic, or lumbosacral paraspinal muscles, flexor pollicis longus, flexor digitorum longus, tibialis posterior, and iliopsoas. Following needle EMG, ultrasound of the muscles-of-interest was performed to determine the presence or absence of hematoma formation. Potential blood-thinning agents, EMG needle size, electromyographer experience level, and time-lapse from EMG to ultrasound also were documented. Statistical analysis was performed using the chi-square test, with P < 0.05 considered significant.
No hematomas were detected among 70 control patients, in whom 100 muscles-of-interest were studied. Among 78 aspirin/clopidogrel patients and 58 warfarin patients, in whom 116 and 107 muscles-of-interest, respectively, were studied, only one hematoma each was seen on ultrasound, in the tibialis posterior and flexor pollicis longus, respectively. In both cases, the hematomas were asymptomatic. In both instances, a 50-mm (26-gauge) needle had been used, in the former by the EMG fellow, in the latter by the attending electromyographer. Telephone follow-up 24 hours later confirmed that the patients remained asymptomatic, with no evidence of bruising or swelling at the site. No significant difference in bleeding rate was found between the three groups (P = 0.43), with only two hematomas found within 323 muscles studied, or 0.62% among the entire study population. Among the warfarin and aspirin/clopidogrel groups, bleeding risk was 0.93% and 0.85%, respectively. Though caution always must be exercised, needle EMG, even of deep muscles, appears safe to perform among patients taking therapeutic doses of antiplatelet agents or anticoagulants. Should the INR be > 3.0, discretion remains the better part of valor.
Commentary
As an interesting and relevant finding, the authors note that ultrasound of the flexor digitorum longus and tibialis posterior muscles, the only ones to develop hematoma formation, incidentally revealed the presence of multiple veins within and surrounding the muscle. Since it is impossible to determine the presence and location of veins in advance of a routine EMG study, their penetration with the EMG needle may predispose these particular muscles to bleeding. It behooves electromyographers to be aware of this anatomy, and a lighter touch might be warranted when studying these muscles, particularly in anticoagulated patients.
References
1. Gruis KL, et al. Survey of electrodiagnostic laboratories regarding hemorrhagic complications from needle electromyography. Muscle Nerve 2006;34:356-358.
2. Bolton CF, et al. Minimum standards for electromyography in Cananda: A statement of the Canadian Society of Clinical Neurophysiologists. Can J Neurol Sci 2000;27:288-291.
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