Isolated Unilateral Temporalis Muscle Hypertrophy: Comprehensive Literature Review.

Abstract

Isolated unilateral temporalis muscle hypertrophy (IUTMH) is a rare clinical entity, with fewer than 20 cases reported globally. This case report and literature review aimed to expand the understanding of its diagnosis, management, and outcomes. A 44-year-old Arab Asian woman presented with a 12 month history of progressive left temporal swelling and pain during mastication. Clinical examination revealed a firm, non-tender mass. Imaging [computed tomography (CT) and ultrasonography] confirmed isolated left temporalis muscle hypertrophy without neoplastic or inflammatory features. Botulinum toxin type A (Btx A, 25 U) injection led to symptom improvement and partial muscle reduction at 3 month follow-up. A literature review of 16 published cases (including ours) demonstrated a slight female predominance (10/16), variable symptom profiles (painless swelling to masticatory dysfunction), and diverse management strategies. Minimally-invasive Btx A achieved favorable outcomes in 6/16 cases, with lower doses (25 U) showing efficacy comparable with higher doses. Surgical intervention, although effective, was associated with recurrence in 1 case. Diagnostic reliance on imaging (CT/magnetic resonance imaging) and histology (when performed) confirmed hypertrophy without malignancy. While bruxism and stress were implicated in some cases, 7/16 lacked identifiable triggers, suggesting multifactorial etiology. Long-term follow-up data remain limited, underscoring the need for vigilant monitoring. This case reinforces Btx A as a primary therapeutic option and highlights the importance of individualized management in IUTMH. Further research is warranted to elucidate pathogenesis and optimize treatment protocols.