The initial instance of isolated unilateral temporalis muscle hypertrophy (IUTMH) was reported in 1990. Since then, only few cases have been documented. The cause of this condition remains ambiguous; however, it is presumed to be linked to compensatory and stress-induced hypertrophy. We introduce a rare case of the diagnosis and treatment of IUTMH. A 39-year-old woman presented with a steadily enlarging pain-free swelling on the left side of her face, first noticed a month ago. Apart from a hyperthyroidism medication regimen her medical history was unremarkable. She had no history of temporomandibular joint disease, bruxism, surgery, or trauma. However, she complained of having been under substantial stress lately. Contrast-enhanced magnetic resonance imaging revealed asymmetric temporalis muscle hypertrophy. The treatment plan consisted of administering type A botulinum toxin injections into left temporalis muscle, supplemented by lifestyle changes and relaxation techniques. At a follow-up visit 9 months after the injections, the muscle contour was normalized both in physical and in radiologic examinations. While further supportive evidence is needed, it can be anticipated that cosmetic treatment with botulinum toxin, rather than surgical interventions, will become the standard treatment of IUTMH.
Keywords: Botulinum toxin, type A; Case reports; Hypertrophy; Mastyicatroy muscles; Temporalis muscle.