Medical Toxin Beyond the Face

Botulinum toxin was a neurology drug before it was a beauty drug. Blepharospasm, cervical dystonia, spasticity, hyperhidrosis, migraine — the cosmetic use was the accident, not the intention.

For the injector, that history is useful. It means there is decades of dosing data outside the glabella, and it means the patients who benefit most from your needle may be the ones who never asked for a smoother forehead.

This chapter covers therapeutic toxin: masseter and bruxism, temporalis, hyperhidrosis, and myofascial trigger points. It assumes you already understand muscles of expression and lower-face logic.

UNITS, BRANDS AND DILUTION
A unit is not a unit. Say which product you mean.

Units are brand-specific and are not interchangeable. A unit of one product is not a unit of another. All doses in this chapter are quoted in onabotulinumtoxinA (Botox) units unless stated otherwise.

Dilution logic

• Concentrated (100 units in 1–1.25 ml): small diffusion field. Use where precision matters — perioral, DAO, mentalis.
• Standard (100 units in 2–2.5 ml): the everyday facial dilution.
• Dilute (100 units in 4–10 ml): deliberately wide diffusion. Use for hyperhidrosis, where you want a field effect across sweat glands rather than a point effect.

Dilution changes the field, not the potency. The same total units in a larger volume will spread further, reach more targets, and carry more risk of affecting a neighbour you did not intend to treat.

THE MASSETER — BRUXISM AND LOWER-FACE WIDTH
Pain, teeth and jawline — three results from one muscle.

The masseter is the most rewarding therapeutic muscle in the face. It treats pain, protects teeth, and narrows the lower third — three benefits from one injection, and the reason it converts so well among dentists and any practitioner who sees a high volume of patients.

Marking the safe zone

• Ask the patient to clench. Palpate and outline the muscle belly with a marker.
• Draw three lines: the anterior border of the muscle, the posterior border (roughly the tragus to the mandibular angle), and the inferior border of the mandible.
• Draw a horizontal line from the corner of the mouth to the ear lobe. Stay below it. Above that line the risorius and zygomaticus fibres sit superficially and are the usual cause of an asymmetric smile after masseter treatment.
• Stay at least 1 cm above the mandibular border to avoid the marginal mandibular nerve and the facial vessels at the antegonial notch.

Technique

• 30G or 32G needle, perpendicular to the skin, advanced until it touches bone, then withdrawn 1–2 mm. The masseter is thick; superficial injection wastes the dose in the SMAS.
• Three points per side in a triangle within the lower posterior belly is the standard pattern. Five points for very hypertrophic muscles.
• Do not inject the deep masseter belly independently unless you have specific training — over-treatment there produces a hollow at rest.

Counselling

• Pain relief typically begins at 1–2 weeks. Visible narrowing takes 6–12 weeks because it requires muscle atrophy, not just paralysis.
• Duration is 4–6 months, longer than facial aesthetic toxin, because the muscle is large and the dose is high.
• Warn about transient chewing fatigue in the first fortnight, particularly with tough foods.
• Warn about paradoxical bulging on clenching if the superficial belly is treated and the deep belly compensates.
• Repeated high-dose treatment over years can reduce bone stimulus at the mandibular angle. Reduce maintenance doses accordingly.

TEMPORALIS AND ORO-FACIAL PAIN
Treat the masseter alone and the load just moves upstairs.

Treating the masseter alone in a heavy bruxer often shifts the load into the temporalis, and the patient returns saying the jaw is better but the headaches are worse. Treating both is usually the more complete answer.

• Dose: 15–25 Botox units per side, spread over 4–6 points across the palpable belly within the temporal fossa.
• Depth: into muscle, above the deep temporal fascia. Stay a finger's breadth above the zygomatic arch and behind the temporal fusion line.
• Avoid the anterior temporal region close to the lateral orbital rim, where diffusion into the frontalis or lateral orbicularis causes brow asymmetry.
• Do not confuse this with temple volumising, which is a filler procedure in a different plane — see the temple.

AXILLARY HYPERHIDROSIS
The most life-changing thing toxin does, and nobody photographs it.

The single best-evidenced therapeutic use of toxin outside neurology, and the one that changes lives most visibly. Primary focal axillary hyperhidrosis is a licensed indication in most markets.

Mapping: the Minor starch-iodine test

1. Dry and shave the axilla. Ask the patient to stop antiperspirant for 24 hours.
2. Paint the area with iodine solution and allow it to dry completely.
3. Dust with cornstarch.
4. Within 5–10 minutes, active sweat glands turn the starch blue-black. Outline the stained territory with a marker and photograph it.
5. Grid the marked area at approximately 1.5–2 cm intervals.

Injection

• Dose: 50 Botox units per axilla, distributed over 10–20 points (approximately 2.5–5 units per point).
• Dilution: 100 units in 4 ml normal saline — deliberately dilute for field spread.
• Depth: intradermal, raising a visible bleb. Sweat glands sit at the dermal–subdermal junction; subcutaneous injection wastes the dose.
• Needle: 30G or 32G, bevel up, at a shallow angle of about 45 degrees.
• Onset: 3–7 days. Duration: 6–9 months, often longer than facial toxin.

PALMAR AND PLANTAR HYPERHIDROSIS
Effective, painful, and easy to overdose into weakness.

Effective, but harder in every respect: more painful, higher dose, and a real risk of intrinsic hand weakness.

• Dose: 100 Botox units per palm, over 30–50 intradermal points on a 1–1.5 cm grid.
• Anaesthesia is mandatory — median and ulnar wrist blocks, or ice and vibration with a very fine needle in a stoical patient. Topical anaesthetic alone is inadequate on palmar skin.
• Warn about grip weakness — a transient reduction in thumb and finger pinch strength occurs in a meaningful minority and can last several weeks. Counsel musicians, surgeons and manual workers carefully, and consider treating one hand at a time.
• Soles: 100–150 units per sole; thicker stratum corneum means deeper intradermal placement and worse pain. Duration is often shorter.

CRANIOFACIAL SWEATING AND COMPENSATORY PATTERNS
Superficial, wide, and two centimetres clear of the brow.

• Forehead and scalp: 50–100 units in a wide grid, intradermal. The critical caution is diffusion into the frontalis, which causes brow ptosis. Keep injections superficial, stay 2 cm above the brow, and warn the patient that some frontalis softening is likely.
• Frey syndrome (gustatory sweating after parotid surgery): map with starch-iodine, then 20–50 units intradermally. Results are excellent and durable.
• Compensatory sweating after sympathectomy responds poorly and should be managed with realistic expectations.

TRIGGER POINTS AND MYOFASCIAL PAIN
Second line, after the cheaper things have failed.

A myofascial trigger point is a palpable taut band within a muscle that reproduces the patient's referred pain on compression. Toxin is a second-line option after dry needling, physiotherapy and local anaesthetic infiltration have been tried.

• Dose: 10–25 units per trigger point, typically 20–50 units per muscle group, with a pragmatic session ceiling around 200–300 units depending on indication and patient.
• Common targets: upper trapezius, levator scapulae, splenius capitis, sternocleidomastoid, suboccipitals, and the pterygoids in temporomandibular disorder.
• Technique: pincer-grasp the taut band, inject directly into the nodule, and confirm reproduction of the referred pain before injecting.
• Neck caution: injecting the anterior and deep neck muscles risks dysphagia and neck extensor weakness. Keep total posterior neck dosing conservative.
• Chronic migraine has its own validated protocol (155 units across 31 fixed sites), which is covered separately in the headache and migraine pathway.

CONSOLIDATED DOSING TABLE
Every number in this chapter, in one place.

SAFETY, CONTRAINDICATIONS AND GOVERNANCE
The paperwork that makes it medicine rather than a service.

• Absolute contraindications: known hypersensitivity to the toxin or excipients, infection at the injection site.
• Relative: neuromuscular junction disorders (myasthenia gravis, Lambert–Eaton, motor neurone disease), aminoglycoside therapy, pregnancy and breastfeeding.
• Therapeutic doses are high. Keep a running total across all sites in a session and observe a minimum interval of twelve weeks between treatments to reduce the risk of neutralising antibodies.
• Distant spread is dose-related. It is a real, if rare, consideration at therapeutic dosing and should be part of consent.
• Prescribing: toxin is a prescription-only medicine. It must be prescribed for a named patient after a face-to-face assessment by the prescriber.

Final Word

Therapeutic toxin is where aesthetic practice earns its medical credentials. A patient who stops grinding their teeth, or who can wear a shirt in July without planning around it, does not describe you as a cosmetic practitioner. They describe you as their doctor.