ORIGINAL RESEARCH Quantitative Electromyography in Dengue-Associated Muscle Dysfunction Jayantee Kalita,* Usha K. Misra,* Pradeep K. Maurya,* Surala K. Shankar,† and Anita Mahadevan† Purpose: This study was undertaken to document the muscle involvement in dengue virus infection using quantitative electromyography (QEMG). Methods: The patients with dengue myopathy were subjected to clinical examination including muscle power, tone, reflex, and sensations. Blood counts, hemoglobin, hematocrit, serum creatine kinase (CK), and electrolytes were determined. The QEMG was performed in the biceps using multimotor unit potential analysis program. Muscle biopsy was done in two patients. At 1 month, their clinical and QEMG analyses were repeated. Results: Thirteen patients whose median age was 34 years were included. Seven patients had severe and six had mild weakness, which was more marked in proximal lower limb muscles. The median CK level was 480 (300–2,477) U/L. Needle EMG did not reveal any spontaneous activity. The motor unit potentials (MUPs) were of normal to short duration, polyphasic with normal interference pattern. The QEMG revealed a significant change in the duration of MUP at 1 month compared with that of baseline. All the patients clinically and biochemically improved after 1 month. Muscle biopsy revealed interstitial hemorrhage with occasional myonecrosis and myophagocytosis without inflammation or vasculitis. Conclusions: The QEMG in dengue myopathy revealed improvement in the duration of MUP at 1-month follow-up, which paralleled with clinical and CK improvement. Key Words: Dengue, Muscle involvement, Myopathy, Myositis, CK, EMG, Outcome. (J Clin Neurophysiol 2012;29: 468–471) D engue is a mosquito-borne disease prevalent in tropical and sub- tropical regions. Approximately 50 to 100 million cases of dengue fever and 250,000 cases of dengue hemorrhagic fever occur annually (Nathan and Dayal-Drager, 2006). The patients with dengue virus infection present with fever, headache, rash, and myalgia. Recently, muscle involvement in dengue virus infection has been reported based on clinical, laboratory, and experimental studies (Kalita et al., 2005; Malheiros et al., 1993; Misra et al., 2006; Warke et al., 2008). Serum CK although is elevated to a variable extent in dengue-associated muscle disease, but EMG characteristically does not show spontane- ous activity, which is a marker of inflammatory muscle disease. Mus- cle histology also has not revealed necrotizing changes (Malheiros et al., 1993; Sangle et al., 2010; Misra et al., 2012). Dengue-associated muscle disease has a relatively benign course and recovers in a period of 1 to 4 weeks. Sequential EMG studies may help in understanding the pathophysiology of muscle disease in dengue virus infection. Visual analysis of concentric needle EMG is a subjective evaluation and is operator dependent. The QEMG differentiates neurogenic changes from myopathic changes as accurately as histology does (Buchthal and Kamieniecka, 1982). It can objectively measure the extent of muscle involvement. The QEMG has not been used so far in the evaluation of viral myositis. In this communication, we report for the first time the sequential QEMG findings in dengue-associated muscle disease and their follow-up. SUBJECTS AND METHODS Thirteen patients with dengue-associated muscle disease have been included in this study, who consented for participating in the QEMG study. The diagnosis of dengue myopathy was based on fever, weakness, increased CK, and positive dengue serology. The patients were subjected to clinical and neurologic examination including the presence of petechiae, ecchymosis, lymphadenopathy, hepatosplenomegaly, and conjunctival congestion. Muscle tender- ness was noted. Muscle power was graded on a 0 to V MRC (Medical Research Council) scale. Muscle tone, tendon reflex, sensations, and coordination were tested. The patients were investigated for total white cell count, hemoglobin, hematocrit, prothrombin time, activated partial throm- boplastin time, blood sugar, serum creatinine, bilirubin, transami- nase, lactic dehydrogenase, sodium, potassium, calcium, and CK. Electromyography Concentric needle EMG was carried out in the biceps, deltoid, vastus lateralis, and tibialis anterior on the right side when platelet counts were .40,000/mm 3 , and coagulation test results were found to be normal. The presence of spontaneous activity such as fibrilla- tions, positive sharp waves, and complex repetitive discharges were noted. The MUPs were visually analyzed for duration, shape, phase, and interference pattern. Quantitative MUP analysis was performed in the biceps using multi-MUP analysis program using a four-channel electromyograph (Synergy, Oxford, United Kingdom). Multimotor unit potential analysis is an advanced automatic technique used for QEMG and interference pattern analysis. This technique helps in collecting more MUPs in a short time and allows not only low threshold early recruiting MUPs but also later recruited units with less bias in the selection of MUPs. The patients were instructed to exert mild to moderate power during the acquisition of MUPs. After acquisition of 20 MUPs, the measurements of MUPs were visually verified before recording their mean duration, amplitude, area, turn, area-to- amplitude ratio, phase, polyphasia, and firing rate. Muscle biopsy of the left vastus lateralis was done under local anesthesia once the platelet count and coagulation parameters were From the *Department of Neurology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Lucknow, India; and †Department of Neuropathology, NIMHANS, Bangalore, India. Address Correspondence and reprint requests to Usha K. Misra, MD, DM, Department of Neurology, Sanjay Gandhi Post Graduate Institute of Medical Sciences, Raebareily Road, Lucknow 226014, India; e-mail: drukmisra@ rediffmail.com. Copyright Ó 2012 by the American Clinical Neurophysiology Society ISSN: 0736-0258/12/2905-0468 468 Journal of Clinical Neurophysiology  Volume 29, Number 5, October 2012