Cervical dystonia is a neuromuscular condition that causes the affected neck musculature to contract involuntarily, inducing abnormal head posture and head movements that often involve pain and difficulties in performing daily tasks. The major treatment approaches include rehabilitation and medications, BoNT injections, and surgery on rare occasions, with BoNT undoubtedly the most favoured option. Muscles commonly injected include the splenius capitis, sternocleidomastoid, trapezius, and others (Brashear 2001).

The starting dose usually follows a common regimen, e.g., 500 IU Dysport®. Re-dosing depends on the clinical response to treatment. Total doses vary during the same session, with Dysport® averaging approximately 652.5 IU per session and Botox® around 159.5 IU, with Xeomin® doses equivalent to Botox doses (Comella and Thompson 2006).

Common side effects are generally mild and transient, including dysphagia, neck weakness, and discomfort. Therefore, treatment is individualised to provide maximal benefit to the patient while minimising side effects. Improvement in symptoms, with sustained benefits over time, indicates that BoNT injections have positive effects (Hauser et al. 2013).

Involuntary constriction of the eyelid muscles (the orbicularis oculi, corrugator, and procerus), resulting in chronic eyelid closure, is a focal dystonia-like condition called blepharospasm. BoNT-A has always been the first-line treatment for this condition. Injections of BoNT-A predominantly target the orbicularis oculi muscle, which is responsible for the closure of the eyelids. Doses vary between 15 and 42.5 IU per session. BoNT-A is highly effective in 86% of patients, who reported good to excellent results (Chauhan et al. 2013). Common side effects include weakness of the orbicularis oculi muscle, ptosis, dry eye, and ecchymosis, which are transient and generally mild (Jochim et al. 2020).

Post-stroke spasticity is characterised by an abnormal increase in muscle tone due to a pathology within the central nervous system. This condition interferes with voluntary movements, particularly those related to motor functions. BoNT is administered to reduce muscle tone in patients with chronic spasticity following neurological injury (Santamato et al. 2015).

BoNT-A provides a noticeable reduction in muscle tone and spasticity in both the upper and lower limbs following a stroke. It is regarded as safe, with adverse effects being rare and generally mild. The gastrocnemius is the most commonly treated muscle for lower limb spasticity, while several flexor muscles are typically targeted for upper limb spasticity (Santamato et al. 2015).

The choice of specific muscles and dosage depends on the severity and location of the spasticity. Guidelines suggest a maximum of 600 IU of onabotulinumtoxinA/incobotulinumtoxinA or 1500 IU of abobotulinumtoxinA to minimise the risk of significant adverse events (Brashear et al. 2002).

Chronic migraine headaches are effectively managed with BoNT-A. Recent studies demonstrate a reduction in migraine frequency ranging from 0.23 to 1.56 fewer headaches per month (Grazzi and Usai 2015; Bruloy et al. 2019). The PREEMPT protocol, which is the most widely utilised treatment regimen, involves the administration of 155 IU of onabotulinumtoxinA (Botox®) (Begasse de Dhaem et al. 2020). Injections are directed at the frontalis, corrugator supercilii, procerus, temporalis, occipitalis, and orbicularis oculi muscles. The “follow the pain” approach is frequently employed, targeting the muscles where the pain is most intense (Naprienko and Smekalkina 2015).

Hyperhidrosis is characterised by excessive sweating due to the overactivity of sweat glands. BoNT-A effectively manages hyperhidrosis by inhibiting acetylcholine release, thereby reducing sweat production, particularly in the axillary, palmar, and plantar regions (Doft et al. 2012). onabotulinumtoxinA and incobotulinumtoxinA are commonly used, typically administered at doses of approximately 100 IU per side, with effects lasting between 6 and 10 months (Rossel et al. 2013). The use of BoNT-A for treatment is considered safe. Muscle weakness, especially in the hands, may occur but generally resolves within a few weeks (Campanati et al. 2014).

BoNT reduces muscle activity by affecting neuromuscular transmission, and its increasing use has proven effective in treating various gastrointestinal (GI) disorders. The most relevant GI diseases treated with BoNT include:

Achalasia: BoNT injections at the lower oesophageal sphincter help alleviate pressure, improving oesophageal emptying and providing symptomatic relief, especially in patients who are unsuitable for surgery or pneumatic dilation. Typically, 100 IU of BoNT is injected into the lower oesophageal sphincter (Yamaguchi et al. 2015).

Gastroparesis: Delayed gastric emptying is managed by injecting BoNT into the pylorus, reducing pyloric pressure and enabling gastric emptying. This provides symptom relief in cases where other treatments may be ineffective. Doses of BoNT-A range from 80 to 200 IU (DeSantis and Huang 2007).

Hypertonic gastrointestinal disorders: Certain spastic conditions, such as sphincter of Oddi dysfunction or hypertensive oesophageal disorders, can be treated with BoNT injections to relax muscle hypertonia and provide symptom relief by inhibiting acetylcholine release. The exact dosing for these conditions remains less defined, but BoNT is typically used to relax the targeted sphincter and relieve symptoms (Bromer et al. 2005; Vittal and Pasricha 2006).

BoNT has an excellent safety profile, with a low incidence of side effects, making it a valuable option for high-risk patients who are not candidates for invasive procedures. Studies show that about 43% of patients respond to treatment, with a median duration of symptom relief lasting approximately five months (Chen 2012).

Urinary incontinence refers to the involuntary loss of bladder control, often due to dysfunction in the detrusor muscle, the sphincter, or the nerve pathways that regulate urination. OnabotulinumtoxinA is used to treat urinary incontinence resulting from neurogenic detrusor overactivity (NDO) and overactive bladder (OAB).

In NDO, a typical dose of 200 IU is injected into the detrusor muscle, showing efficacy in reducing incontinence and improving urodynamic outcomes in patients with multiple sclerosis and spinal cord injuries (da Silva et al. 2015). For OAB, 100 IU is injected into the detrusor muscle to decrease incontinence, reduce urinary frequency, and enhance the patient’s quality of life (da Silva 2015; Yokoyama et al. 2020).

The injections are administered directly into the bladder, avoiding the trigone area to minimise potential side effects. Despite its strong efficacy, common side effects include urinary tract infections, urinary retention (sometimes requiring catheterisation), and transient muscle weakness or fatigue (Yokoyama et al. 2020).

Although the use of BoNT in treating myofascial pain syndrome remains controversial, some studies provide strong evidence of significant pain relief and enhanced quality of life, while others report no clear benefit over placebo (Cheshire et al. 1994). The dosage of BoNT varies widely across studies, ranging from low doses (5 IU) to high doses (up to 400 IU), which contributes to variability in the results (Göbel et al. 2006; Ojala et al. 2006). Most side effects are mild to moderate and temporary, and BoNT is generally well tolerated. A common adverse effect is muscle weakness (Göbel et al. 2006).

BoNT is a standard treatment for glabellar lines, primarily targeting the corrugator supercilii and procerus muscles. Botox®/Vistabel® and Dysport® typically require 50 IU, administered across five injection sites arranged in a swallow-like pattern (Dorizas et al. 2014). Due to their larger muscle mass, men generally require higher doses, with 40 IU considered the minimum starting dose (Monheit et al. 2007).

BoNT injections are commonly used to treat the frontalis and glabellar muscles, reducing the appearance of forehead wrinkles. Accurate placement of the toxin in the frontalis muscle is crucial to minimise complications such as ptosis. Intramuscular injections are effective but may carry a higher risk of such complications. Intradermal injections reduce this risk but may cause more discomfort during the injection process (Mitra et al. 2024).

Dosage should be tailored to each patient, taking into account muscle mass, anatomical factors, and treatment goals, with particular attention to populations with smaller muscle mass, such as Asians (Hong 2023). For forehead wrinkles, BoNT-A dosing typically involves nine injections, arranged in two rows, with 1 IU per injection site (Yi et al. 2024).

Crow’s feet wrinkles are among the most effectively treated by BoNT, which temporarily paralyses the orbicularis oculi muscle. A typical dose for crow’s feet is approximately 12 IU per side, with injections targeting the lateral aspect of the muscle (Small 2014). Recently, a novel injection technique using ultrasound guidance has been shown to enhance both the precision and efficacy of the treatment (Popescu et al. 2024).

BoNT-A is widely used for the reduction of marionette lines, which are the lines running from the corners of the mouth down to the chin. In a study involving 189 patients, the average dose for treatment was 113.8 IU, with doses ranging from 50 to 180 IU (D’Emilio and Rosati 2020). The treatment is generally well tolerated, with mild complications. Recommendations for treating marionette lines with onabotulinumtoxinA include careful evaluation of the patient’s facial anatomy and muscle activity (Bertossi et al. 2018). Dosing should be individualised based on the severity of the wrinkles and the desired outcome. Combining BoNT-A with other treatments, such as hyaluronic acid fillers, may improve the aesthetic result of marionette lines. This combination can provide a more balanced and natural appearance by addressing both muscle activity and volume loss (Borodic 2013).

BoNT is widely used in aesthetic medicine for eyebrow elevation and correction of gummy smiles. For eyebrow lifting, BoNT is injected into the glabellar region to relax the muscles that pull the brow downward, allowing for a gentle upward movement. The dosage typically ranges from 10 to 40 IU, with injections placed across the glabellar area, extending from the midline to the mid-pupillary line (Carruthers and Carruthers 2007). For a gummy smile, BoNT is injected into the levator labii superioris muscle to prevent excessive gum display when smiling. Typically, 2 IU are administered at each injection site, with 2–4 sites targeted (Costa et al. 2022).

BoNT is commonly used to reduce the appearance of platysmal bands, the vertical lines that develop with age on the neck. The treatment works by relaxing the platysma muscle, which softens the lines and improves the neck’s appearance. Typically, 20 to 50 IU are used, with 2 to 4 IU injected at each site, depending on the thickness of the bands and individual patient anatomy. Injections are administered along the muscle from the angle of the mandible to the clavicle (Obagi and Golubets 2017; Sugrue et al. 2019).