Masticatory muscle hypertrophy is a rare clinical entity involving isolated or combined hypertrophy of all groups of masticatory muscles. Majority are bilateral with rare cases presenting as unilateral [
1‐
3]. Isolated unilateral temporalis muscle hypertrophy is an extremely rare condition. The first case was reported by Wilson and Brown in 1990 [
9]. For the last two decades, there have been only nine cases reported in English literature (Table
1). Based on the variability of age of presentation, there does not appear to be an age predilection for the disease [
10]. Masseter and temporalis muscles can be involved and they may present together or in the setting of isolated, bilateral hypertrophy [
2‐
4,
11]. The exact etiology has not been identified for masticatory muscle hypertrophy. Theoretical explanation is secondary to parafunctional jaw movements [
3]. However, the other causes such as inflammation, trauma, neoplasm, myopathy, muscular dystrophy need to be excluded [
2,
12]. Out of the documented cases the youngest patient with IUTMH was a 15 year old female reported in 1998 [
6]. Present study is seven year old girl with IUTMH, is the youngest child reported to date according to the best of our knowledge.
Isolated unilateral temporalis muscle hypertrophy is peculiar because there is no identifiable etiology, age category or side predominance [
13,
14]. The potential etiological factors for IUTMH include local factors such as bruxism, dental malocclusion, bony prominences leading to trauma and reactive hypertrophy ascribed to psychogenic factors [
13,
14]. The definitive diagnosis is confirmed via histological examination of the affected muscle [
14]. However, In some cases a muscle biopsy was not performed due to various reasons and patients were treated symptomatically [
7]. Regarding treatment there are several treatment modalities available for IUTMH. Some patients have not undergone any active intervention and were treated symptomatically [
6,
15], while others had Botulinum toxin A (BtA) injections [
16,
17], surgical interventions, [
18] or depending on the severity of the symptoms treatment with analgesics [
7,
19]. Even though the cost associated with BtA injection is higher there are several advantages over surgical therapy. The injections are simple and less invasive, no surgical complications like trismus, fibrosis, BtA will temporally paralyze the muscle leading to atrophy, and symptomatic improvement of associated headache [
13,
16‐
18,
20]. In this case, our patient is under regular follow up with symptomatic treatments, including analgesics and regular visual assessments. The parents were informed about the available treatment modalities and chose symptomatic treatment over other definitive treatment modalities due to the benign nature of the condition and the lack of major cosmetic concerns.