Focal Myositis of the Deltoid Muscle: The Role of Magnetic Resonance Imaging for Diagnosis.

INTRODUCTION

Focal myositis is a rare condition first described by Heffner et al., in 1977, as a self-limiting condition of unknown aetiology. It presents as an inflammatory pseudo tumour in skeletal muscle and can present diagnostic difficulty, being commonly mistaken for tissue of vascular, inflammatory, or neoplastic origin. Diagnosis is traditionally confirmed by muscle biopsy. We present a case where magnetic resonance imaging (MRI) was used to confirm the diagnosis without need for biopsy.

CASE PRESENTATION

A 19-year year-old female presented with a two2-year history of intermittent swelling of the deltoid associated with pain and tenderness to palpation. . There was no history of trauma or systemic illness. . She was symptomatic with pain, swelling, and tenderness over the left deltoid with no restriction in range of movement of the shoulder or neck. Plain radiographs were normal and MRI magnetic resonance imaging showed diffuse odeamatousedematous signal changes on the proton density weighted sequence within the deltoid muscle and no plexiform neurofibroma. Nerve conduction and electromyography studies were within normal limits excluding an axillary nerve lesion. The patient underwent extensive screening for connective tissue disorders and creatine kinase and lactate dehydrogenase levels were within limits. The patient underwent neuromuscular specialist review confirming that this appeared to be a rare case of focal myositis in the deltoid. . The serial MRI scans confirmed resolution of the condition.

CONCLUSION

Focal myositis of the deltoid is a rare cause of shoulder pain. . We have shown that sequential MRI scanning can obviate the need for muscle biopsy, which has historically been required for diagnostic confirmation. The MRI appearance on the proton density weighted sequence showed diffuse odeamatousedematous signal changes and no plexiform neurofibroma within the deltoid and is a description that has not been previously used for this rare diagnosis.