Influenza-Associated Myositis in Children

Abstract

Background: Influenza-associated myositis (IAM) is an infrequent and poorly known complication of influenza virus infection in children. The aim of this study was to describe five cases of IAM and to review the literature on IAM in children. Patients and Methods:We conducted a retrospective analysis of cases of IAM diagnosed at two university children's hospitals in Switzerland during two consecutive influenza seasons. Findings were compared with 39 individual case reports and five publications summarizing an additional 272 cases identified by a medical online library (MEDLINE) search. Results: Overall, 316 cases were analyzed. IAM typically occurred in school-aged children with a 2:1 male predominance. Influenza B and A viruses were identified in 76% and 24% of cases, respectively. The median interval between onset of influenza and onset of IAM was 3 days (range 0-18). The calf muscles were involved alone or together with other muscle groups in 69% and 31% of cases, respectively. Blood creatine phosphokinase (CPK) concentration was invariably elevated. Median duration to clinical recovery was 3 days (range 1-30). Rhabdomyolysis occurred in ten of 316 patients (3%), was more common in girls (80%), more often associated with influenza A (86%), and led to renal failure in eight patients (80%). Conclusion: Clinical and laboratory findings of IAM are highly characteristic and allow a rapid diagnosis during the influenza season.

Benign acute childhood myositis: an alarming condition with an excellent prognosis!

“…Most commonly occur after influenza B and occasionally influenza A infection, but parainfluenza, adenovirus, herpes simplex, Epstein-Barr, Coxsackie, rotavirus, and M pneumoniae have also been implicated [1][2][3][5][6][7][8][9][10], as found in our study. As evidenced, key elements in the diagnosis are a preceding upper respiratory infection followed by the acute onset of typical myositis clinical findings, predominantly affecting gastrocnemius-soleus muscles.…”

“…Patients with this typical clinical presentation can be treated as an outpatient [1,5]. However, as seen in our study, some children are admitted for hydration, observation, and serial CK levels to rule out any progression to rhabdomyolysis [1,6,[8][9][10]. Recurrence is rare and has been demonstrated to be caused by different viruses or different influenza types [9].…”

“…As evidenced, key elements in the diagnosis are a preceding upper respiratory infection followed by the acute onset of typical myositis clinical findings, predominantly affecting gastrocnemius-soleus muscles. Further clinical features include school-aged boys and late winter-early spring predominance, elevated CK, and aminotransferase levels (especially AST) [1][2][3][4][5][6][7][8][9][10]. Transient hematological abnormalities (mild leukopenia, neutropenia, and thrombocytopenia) are also seen [1,3,[8][9][10].…”

“…Transient hematological abnormalities (mild leukopenia, neutropenia, and thrombocytopenia) are also seen [1,3,[8][9][10]. Erythrocyte sedimentation rate and CRP are usually normal but may be mildly elevated [1][2][3]5,6]. Patients with this typical clinical presentation can be treated as an outpatient [1,5].…”

“…Patients can be discharged if they have typical presentation, normal renal function, and follow-up to ensure complete resolution [2,10]. Further investigation is not indicated unless there is clinical concern for more serious disorders [1,6,8,10]. Findings not classically associated with BACM include myoglobinuria, recent trauma or vigorous exercise, family history of neuromuscular disorders, subacute or chronic progression, a new rash, frank muscle weakness, or abnormal neurologic findings.…”