Diagnosis of enlarged extraocular muscles: when and how to biopsy.

PURPOSE OF REVIEW: To review current knowledge regarding diagnosis of nonthyroid orbital disorders with extraocular muscle enlargement.

RECENT FINDINGS: Recent publications have focused on immunoglobulin G4-related disease as a possible cause of enlarged extraocular muscles, on patterns of strabismus that raise a clinical suspicion of intramuscular lymphoma, and on surgical techniques to access the muscles for tissue biopsy.

SUMMARY: With enlarged extraocular muscles, features to distinguish between competing diagnostic possibilities are based on imaging in the context of history and clinical signs. Infraorbital nerve enlargement in the presence of muscle enlargement strongly favours a diagnosis of immunoglobulin G4-related disease and reactive lymphoid hyperplasia. As our understanding of minimally invasive orbital surgery evolves, the diagnostic focus is shifting toward earlier identification through muscle biopsy.