Benign acute childhood myositis (BACM) is a syndrome characterized by muscle weakness and pain of the lower limbs that develop in children after a recent viral illness. It is transient with a spontaneous clinical resolution within 1 week.[1][2]
Symptoms
Prodromal symptoms are typically fever, cough, and rhinorrhea. BACM symptoms that follow are most frequently calf pain, gait complaints, and inability to walk.[2] The condition is self-limited and full restitution can be expected. In very rare cases, however, rhabdomyolysis may develop.[1]
Affected are pre-school and school-age children with a male predominance.[2] In one study, the median age was 6 years (range 2-13.2 years).[1] It has been estimated that BACM has an incidence of 2.69 cases per 100,000 children (<18 years) during epidemic seasons and 0.23 cases during non-epidemic seasons.[3]
Diagnosis
The history of a preceding influenza-like infection followed by the typical symptoms of acute onset of symmetrical calf pain and gait problems together with an isolated finding of a high level of creatine kinase suggests the diagnosis of BACM.[4] Myoglobinuria is rare and points to the possibility of rhabdomyolysis.[2]
Guillain-Barre syndrome is the main consideration in the differential diagnosis. Other conditions are dermatomyositis, muscular dystrophy, juvenile idiopathic arthritis, transient synovitis of the hip, osteomyelitis, and myalgia.[1]
Preceding viral infections
A number of different viral infections have been reported, most commonly influenza A and B. The condition appears to be more prevalent during late fall, winter, and spring.[2] Other virus infections that have been linked to BACM are those caused by Parainfluenza, Cocksackievirus, Adenovirus, Echovirus, and Mycoplasma pneumonia.[1]
Management
BACM may be alarming to parents and lead to unnecessary extensive tests.[4] Treatment consists of oral analgesics, rest, and adequate hydration.[1] Hospitalization is usually not necessary. Full recovery can be expected within a week, however, recurrences can occur.
History
in 1957 Lundberg reported on a group of patients with a condition he named myalgia cruris epidemica[5], seemingly the first description of BACM. Other terms later used include influenza-associated myositis, viral myositis, acute myositis[2] Middleton and colleagues reported on BACM as severe myositis after influenza in 1970.[6]