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Masseter hypertrophy facial swelling botulinum toxin treatment

last modified on: Sat, 04/16/2022 - 11:00

Masseter hypertrophy as a cause of facial swelling

return to: Salivary Swelling

Treatment of the case above with Botox®:

  • Improved chewing
  • Diminished pain
  • Prevented  jaw from disengaging or clicking
  • Improved facial contour

through a sequence of three injections to the left masseter (25 units in 1 cc of onabotulinumtoxinA = Botox ®/Botox Cosmetic® (Allergan, Inc) with EMG guidance.  Initial treatment resulted in 3 months of benefit with the second injection more durable but still warranting a third injection one year after the second.


Masseter muscle enlargement (hypertrophy) can be accompanied by pain and is often erroneously ascribed to a disorder of the adjacent parotid gland. An excellent review by Fedorowicz et al (2013) identified potential causes to be 

  • emotional stress
  • chronic bruxism 
  • masseteric hyper-function
  • microtrauma

​In some cases the masseter enlargement is thought to arise from a disorder other than work hypertrophy with the absence of a certain type of muscle fiber supporting a cause other than 'work hypertrophy' 

  • ​clenbuterol (a bronchodilator with growth-promoting properties prohibited in animal husbandry and sport, used to treat reactive airway disease Thevis 2013) induced hypertrophy
  • overuse of anabolic steroids
  • localised scleroderma
  • facial hemi-atrophy (see: (under construction) Hemifacial Atrophy (Parry-Romberg Syndrome PRS) Romberg Syndrome atrophy in trigeminal nerve distribution )
  • multifactorial origin in combination with a genetic basis
  • benign masseter hypertrophy is also compatible with a rare genetic condition known as hypertrophic branchial myopathy 

Recommendations for evaluation have included

  • Computed tomographic (CT) scan, magnetic resonance imaging  (MRI) scan, or both (considered the gold standard in confirming a clinical suspicion).
  • Ultrasonographic measurement.
  • Muscle biopsy.
  • Morphometric analysis
  • Electromyographic measurement.

Reported treatments include:

  • Use of muscle relaxants
  • Bite adjustments or involve the use of splints on the teeth.
  • Surgical reduction of the jaw muscle
  • Injections of botulinum toxin type A directly into the muscle are other treatment options. 
    • The 2013 Cochrane analysis (Fedorowicz 2013) concludes: "Although the use of botulinum toxin injections might appear to have certain advantages over surgery the authors of this review did not find any high quality studies that evaluated the effectiveness and potential side effects of botulinum toxin type A for the management of benign masseter hypertrophy. Well-designed randomised controlled trials are needed to assess the effectiveness and safety (i.e. side effects) of this intervention."

Botulinum Neurotoxin Treatment (BoNT)

Although the largest reported experiences with use of BoNT come from the cosmetic use for facial recontouring, it has been used successfully to treat masseter hypertrophy to address pain associated with unilateral enlargement.

A review (Yeh 2018) addressing publications from January 1994 to Feb 2018 emphasized analysis of complications - that overall were considered rare with the majority appearing with in 2-4 weeks of the injection and disappearing within 12 weeks. 

Yeh et al 2018 Literature Reivew of Adverse ..

        for BoNT Masseter Hypertrophy

Local swelling, bruising, and hematoma
Chewing Weakness
Poor Effect and Asymmetry
Lack of Response
Worsened Jowls or Sagging
Paradoxical Bulging
Changes in Facial Expression
Abnormal Movement of the Temporomandibular Joint
Sunken Cheek
Sunken Temporal Fossa


Capaccio P1,2, Gaffuri M1,3, Pignataro L1,3, Assandri F4,2, Pereira P4,2, Farronato G4,2.Recurrent parotid swelling secondary to masseter muscle hypertrophy: a multidisciplinary diagnostic and therapeutic approach. Cranio. 2016 Nov;34(6):388-394. Epub 2016 Mar 21

Bhattacharjee K1, Singh M1, Bhattacharjee H1Extended effect after a single dose of type A botulinum toxin for asymmetric masseter muscle hypertrophy. Indian J Plast Surg. 2015 May-Aug;48(2):196-9. doi: 10.4103/0970-0358.163061.

Wei J1, Xu H, Dong J, Li Q, Dai C.Prolonging the duration of masseter muscle reduction by adjusting the masticatory movements after the treatment of masseter muscle hypertrophy with botulinum toxinDermatol Surg. 2015 Jan;41 Suppl 1:S101-9. doi: 10.1097/DSS.0000000000000162. type a injection.

Fedorowicz Z1, van Zuuren EJ, Schoones J.Botulinum toxin for masseter hypertrophy. Cochrane Database Syst Rev. 2013 Sep 9;(9):CD007510. doi: 10.1002/14651858.CD007510.pub3.

Kim NH1, Park RH, Park JB.Botulinum toxin type A for the treatment of hypertrophy of the masseter muscle. Plast Reconstr Surg. 2010 Jun;125(6):1693-705. doi: 10.1097/PRS.0b013e3181d0ad03.

Thevis M1Geyer LGeyer HGuddat SDvorak JButch ASterk SSSchänzer W. Adverse analytical findings with clenbuterol among U-17 soccer players attributed to food contamination issues. Drug Test Anal. 2013 May;5(5):372-6. doi: 10.1002/dta.1471. Epub 2013 Apr 4.

Mishra K, Sood A, Smidt A, Price HN   Botulinum toxin A for pain reduction in pediatric patients with Parry-Romberg syndrome. Pediatr Dermatol. 2019 Feb 10. doi: 10.1111/pde.13746. [Epub ahead of print]

Yeh YT, Peng JH, Peng HP. Literature review of the adverse events associated with botulinum toxin injection for the masseter muscle hypertrophy.  J Cosmet Dermatol. 2018 Oct;17(5):675-687. doi: 10.1111/jocd.12721. Epub 2018 Aug 9.

Kim NH1, Park RH, Park JB Botulinum toxin type A for the treatment of hypertrophy of the masseter muscle.   Plast Reconstr Surg. 2010 Jun;125(6):1693-705. doi: 10.1097/PRS.0b013e3181d0ad03.

Shin SH, Kang YJ, Kim SG. The effect of botulinum toxin-A injection into the masseter muscles on prevention of plate fracture and post-operative relapse in patients receiving orthognathic surgery. Maxillofac Plast Reconstr Surg. 2018 Nov 25;40(1):36. doi: 10.1186/s40902-018-0174-0. PMID: 30538972; PMCID: PMC6261083.