Trismus, or Lockjaw, refers to reduced opening of the jaws caused by spasm of the muscles of mastication, or may generally refer to all causes of limited mouth opening.

It is a common problem with a variety of causes, and may interfere with eating, speech, oral hygiene, and could alter facial appearance. There is an increased risk of aspiration. Temporary trismus is much more common than permanent trismus, and may be distressing and painful, and limit or prevent medical examination or treatments requiring access to the oral cavity.

Feinberg et al present a case of Chiari malformation manifesting as isolated trismus, describe the typical symptoms associated with Chiari malformation, and discuss the potential anatomical causes for this unique presentation. A 3-year-old boy presented with inability to open his jaw for 6 weeks with associated significant weight loss. The results of medical and radiological evaluation were negative except for Chiari malformation type 1 with cerebellar tonsils 12 mm below the level of the foramen magnum. The patient underwent Chiari decompression surgery. Postoperatively, his ability to open his mouth was significantly improved, allowing resumption of a regular diet. Postoperative MRI revealed almost complete resolution of the syringobulbia. To the best of the authors' knowledge, this is the first reported case of isolated trismus from Chiari malformation with syringobulbia ¹⁾.