title: Influenzavirus B-associated acute benign myalgia cruris: an outbreak report and review of the literature.
abstract: Acute benign myalgia cruris is characterized by transient bilateral calf pain that leads to difficulty walking. A regional outbreak of influenza virus B-associated myalgia cruris was observed during the seasonal influenza outbreak observed in Switzerland from week 1 to 13 of 2013. We performed a prospective case finding among the Swiss-Italian pediatric emergency units and pediatricians. A review of the literature was also performed. The diagnosis of myalgia cruris was made in 49 Swiss-Italian children aged 3.0-14 years (♂:♀=1.7). Flu-like symptoms were resolving when bilateral calf pain began that remitted over ⩽ 7days. The creatine kinase-level, assessed in 28 patients, was elevated in 25. Nose swabs were positive for influenza virus B in 13 out of 14 cases. The blood cell count, measured in 41 cases, disclosed leucopenia in 12 and thrombocytopenia in 3. The review of the literature found 10 outbreaks of ⩾ 10 cases of influenza virus B-associated myalgia cruris, which included a total of 203 patients with a mean age of 7.3 years and a ♂:♀ ratio of 2.0. In conclusion influenza virus B caused a large Swiss-Italian outbreak of myalgia cruris. Our outbreak and the literature indicate that influenza virus B-associated myalgia cruris affects preschool- and school-aged children, primarily boys.
authors: Integrated Department of Pediatrics, Ente Ospedaliero Cantonale Ticinese, and University of Berne, Switzerland.
authors: Alessandra
authors: A
authors: Ferrarini
authors: Integrated Department of Pediatrics, Ente Ospedaliero Cantonale Ticinese, and University of Berne, Switzerland.
authors: Sebastiano A G
authors: SA
authors: Lava
authors: Integrated Department of Pediatrics, Ente Ospedaliero Cantonale Ticinese, and University of Berne, Switzerland.
authors: Giacomo D
authors: GD
authors: Simonetti
authors: Integrated Department of Pediatrics, Ente Ospedaliero Cantonale Ticinese, and University of Berne, Switzerland.
authors: Gian Paolo
authors: GP
authors: Ramelli
authors: Integrated Department of Pediatrics, Ente Ospedaliero Cantonale Ticinese, and University of Berne, Switzerland. Electronic address: mario.bianchetti@pediatrician.ch.
authors: Mario G
authors: MG
authors: Bianchetti
mesh_terms: D002648:Child; D002675:Child, Preschool; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D007251:Influenza, Human / Q000453:epidemiology* / Q000503:physiopathology*; D029524:Betainfluenzavirus; D007558:Italy / Q000453:epidemiology; D008297:Male; D009069:Movement Disorders / Q000453:epidemiology / Q000503:physiopathology; D063806:Myalgia / Q000453:epidemiology* / Q000503:physiopathology*; D013557:Switzerland / Q000453:epidemiology
keywords: Acute benign myalgia cruris; Acute toe walking; Benign childhood myositis; Bottom shuffling; Frankenstein walk; Influenza virus B; Review