The objective of this study was to assess the efficacy of Botulinum toxin type (A) (BoNTA) injection in Myofascial pain syndrome management in the terms of duration of function improvement and pain reduction.

Material and methods: Fourteen patients with Myofascial pain syndrome related to masticatory muscles were presented with trismus, pain and impairment of oral function. Treatment plan was established by utilizing thirty units of Botulinum toxin type (A) which was injected into masseter and sometimes temporalis muscle.

Myofascial pain syndrome (MPS) is acute or chronic musculoskeletal pain that characterized by the presence of unique trigger points of pain (TrPs) . Etiology of this condition may include psychogenic stress, prolong muscle strain, trauma to the joint or muscle, arthritis, myositis, chronic infection, and general fatigue. Current therapeutic approaches available for Myofascial pain syndrome involved pharmacological and non-pharmacological treatment options. The non-pharmacological techniques may include a) manual therapy by muscle stretch or massage, b) muscular taut band injection by local anesthesia or botulinum toxin, c) acupuncture, and d) therapeutic ultrasound .

Botulinum toxin is a neurotoxin protein produced by anaerobic bacteria (clostridium botulinum) . It was first discovered by a German physician named Justinus Kerner who observed that the toxin acts by impeding signal transmission in the somatic and autonomic motor systems, leaving the sensory signal transmission uninterrupted .

It blocked the acetylcholine release from the nerve endings thus prevent the neurological signals transmission at the neuromuscular junction. In turn, this reduces the muscle contraction and produces relaxation of the muscle . However, the clinical effects of Botulinum toxin are transit as these neurotoxins degenerate at nerve terminals and became inefficient after a period of time .

Although numerous articles were published on the Botulinum Toxin A (BoNTA) injection in the management of MPS, but there were diverse clinical results in the literature regarding this subject and its effectiveness is still questionable . The objective of this study was to evaluate the efficiency and outcomes of BoNTA injection in the management of MPS related to masticatory muscles.

Inclusion Criteria:

1. Patient with myofascial pain related to the muscles of mastication (masseter and temporalis muscle).
2. Patient with regional pain.
3. Patient with or without limited mouth opening (trismus).
4. Presence of trigger points within the identified masticatory muscles.

Exclusion Criteria:

- 1. Hypersensitivity to Botulinum toxin. 2. Active infection in the virtual points of injection. 3. Patient with generalized musculoskeletal pain as in Fibromyalgia Syndrome (FMS).

4. Children younger than 12 years old and pregnant woman. 5-Patient recently undergone to one other modality of treatment