Clinical Characteristics of Epidemic Myalgia Associated with Human Parechovirus Type 3 during the Summer of 2019

OBJECTIVE: Epidemic myalgia associated with human parechovirus type 3 (EM-HPeV3) is characterized by severe muscle pain and weakness on the limbs and trunk with a fever. No outbreak of EM-HPeV3 has been reported since 2016, and its clinical characteristics have not been sufficiently clarified. We herein report a series of EM-HPeV3 cases during the summer of 2019 and clarify the clinical characteristics of EM-HPeV3. METHODS: The diagnosis of EM-HPeV3 was established when the patients met both of the following criteria: (1) Patients developed severe muscle pain and weakness with a fever within a week, and those symptoms resolved within a month; and (2) HPeV3 was detected in either a throat swab or fecal specimen of the patient by polymerase chain reaction. We reviewed the medical records of these patients retrospectively. RESULTS: Seven patients met the criteria (6 men and 1 woman, age 34 to 47 years old). Myalgia was observed on the thigh, lower legs, upper arms, and forearms in seven, five, two, and five patients, respectively. Four patients showed distal dominant weakness on the arms, while none of the patients showed proximal dominant weakness on the arms. Of the six patients examined, five showed reduced tendon reflexes on all four limbs. One patient showed slight myogenic change and increased insertion activities on needle electromyography. CONCLUSION: We observed seven cases of EM-HPeV3 during the summer of 2019. Reduced tendon reflexes and distal dominancy of muscle pain and weakness on the arms are considered its distinct clinical features.