Letter to the Editor

Abstract

11 November 2009 Dear Editor, RECURRENT FOCAL MYOSITIS IN AN INFANT: A REPORT OF THE YOUNGEST CASE Focal myositis (FM) is a benign inflammatory pseudo-tumour of skeletal muscle. Focal enlargement is usually self-limiting without recurrence. Very few recurrent FM cases have been reported in adults.1-3 In addition, three paediatric cases of recurrent FM (9-year-old boy,4 12-year-old boy5 and 15-year-old boy1) have been reported thus far. We describe here a 5-month-old girl who developed recurrent FM originating from the left temporal muscle. To our knowledge, this is the first report of recurrent FM in an infant. The patient was born to healthy parents via Caesarean section at the gestational age of 38 weeks and 5 days because of fetal distress. The patient had no siblings. At the age of 3 months, she received a Bacille de Calmette et Guerin (BCG) vaccination. At the age of 5 months, the mother observed a painful swelling in the left temporal region of the infant. There was no previous history of trauma. Physical examination revealed a firm mass measuring 5 cm in diameter over the left temporal bone. No neurological deficit was observed. Otitis media was excluded. Blood chemistry showed a marked elevation in creatine kinase (CK) (633 IU/mL, reference value 13–33) and a mild increase in aspartate aminotransferase (AST) (48 IU/mL, reference value 6–27). C-reactive protein was slightly elevated. Anti-nuclear antibody, angiotensin-converting enzyme and anti-Jo-1 antibody levels were within their normal ranges. Complete blood count analysis did not reveal significant changes. Eosinophilia was not seen. Contrast-enhanced T1-weighted magnetic resonance imaging (MRI) with fat suppression showed an enlarged muscle of the left temporal region and increased signal intensity within the left temporal muscle (Fig. 1). The left temporal swelling resolved after 1 week of treatment with a cephem antibiotic, Cefazolin (Astellas Pharma Inc., Tokyo, Japan). Contrast-enhanced T1-weighted magnetic resonance imaging depicting an increased signal intensity within the left temporal muscle (arrow head). At 6 months of age, the right temporal muscle was swollen. Serum CK level was elevated (CK 735 IU/mL). MRI depicted an increased intensity in the right temporal muscle. The swelling mass gradually resolved after 1 month. At 8 months of age, swelling of the right forearm was observed. The swelling was found to be a firm mass measuring 2 cm in diameter, which disappeared spontaneously after 1 week without specific treatment. Shortly after the disappearance of the right forearm mass, a few swollen masses appeared on the bilateral soles. No biopsies of the affected muscles were performed because of the absence of consent from the parents. No signs of polymyositis and dermatomyositis (e.g. fever, skin rashes and muscle weakness) had developed throughout the patient's clinical course. FM localised frequently in the lower limb (thigh and lower leg), and in temporal muscles in a few cases.6 The clinical course, the result of laboratory tests and the MRI findings of our patient were consistent with the diagnosis of recurrent FM. Treatment for recurrent FM has not been established. Several treatment options have been attempted, including non-steroidal anti-inflammatory drugs, methotrexate and methylprednisolone; however, no consistent results have been obtained thus far.2, 4 The aetiology of recurrent FM remains unknown. Manganelli et al.2 reported a case of a 22-year-old man who developed bilateral recurrent FM of the gastrocnemius muscles 3 weeks after receiving BCG vaccination. Our patient was administered BCG vaccination 2 months prior to the swelling of the left temporal muscle. In Japan, BCG vaccination is given to more than 1 million infants annually. However, recurrent FM has not been reported in Japanese children thus far. Therefore, if BCG vaccination is a possible trigger for recurrent FM, then host defence mechanisms might be associated with the development of the disorder. Interestingly, FM was reported to have developed in monozygotic twins. Recurrent FM occurred in one of the identical twins, while the other twin developed non-recurrent FM.3 Further studies are necessary to identify genetic and environmental factors associated with recurrent FM.