Nerve injury after injectables: signs and management

Nerve injury is a rare complication in HOF, but it comes up in office conversations more often than in the statistics, because patients describe sensations they cannot name: numbness, shocks, pulling, a "crooked mouth." It is up to the professional to separate what is an expected effect, what is transient and what deserves investigation.

The text is a review and guides reasoning, without replacing clinical assessment or prescribing treatment. The approach in each case belongs to the qualified professional, according to the rules of their professional council in Brazil, and persistent or motor cases call for referral.

Which nerves are part of this conversation?

Two systems hold the relevant anatomy.

Trigeminal nerve (trigeminal nerve). Responsible for sensation in the face. The branches that appear most in HOF are the infraorbital nerve (infraorbital region, side of the nose and upper lip), the mental nerve (lower lip and chin) and the supraorbital and supratrochlear nerves (forehead and glabella).

Facial nerve (facial nerve). Responsible for the movement of facial expression. Its temporal, zygomatic, buccal and marginal mandibular branches innervate the muscles of expression. The marginal mandibular branch is the one most associated with changes in the lower smile.

What distinguishes the sensory picture from the motor one?

An important note: not everything motor is an injury. Muscle blockade by botulinum toxin is a pharmacological effect and, when it occurs outside the target muscle, requires its own management. The pictures of complications with botulinum toxin and ptosis after toxin have a separate page.

How does the injury happen?

The mechanisms described in the review literature include:

• Direct trauma from the needle or cannula, when there is contact with the nerve or its sheath.
• Compression by injected product or by swelling, which can cause transient paresthesia.
• Hematoma, which compresses structures and makes the picture harder to read (see expanding hematoma in the face).
• Local anesthesia or blocks which, by definition, cause temporary numbness, as in the infraorbital nerve block and the mental nerve block.
• Ischemia from vascular occlusion, which can secondarily affect the nerve.

This does not mean every procedure carries the same risk. It means that the anatomy of the emergence points, the choice of instrument and the response to intense pain during injection are part of prevention. The warning is in intense pain during injection: a warning sign.

How do you examine when the patient reports the symptom?

A short sequence that is always the same prevents omissions.

1. Listen and record the complaint in the patient's own words, with onset date and relation to the procedure.
2. Compare the sides at rest and in motion, with the patient seated and adequate light.
3. Test sensation in the suspected area with light touch and pinprick, comparing with the opposite side and neighboring areas.
4. Test movement by asking the patient to smile, frown, raise the eyebrows, squeeze the eyes shut and show the teeth.
5. Look for associated causes: hematoma, significant swelling, vascular signs (pallor, lace-like pattern), infection.
6. Photograph using the standardized protocol and, when it makes sense, record a short video of the movement, with consent. See standardized clinical photography.

What is the expected course?

Mild sensory changes related to anesthesia, swelling or compression are usually transient. Pictures caused by direct trauma vary, and the recovery time is not predictable. It is prudent not to promise a timeframe. What can honestly be said is that follow-up will be done and the condition will be reassessed.

Motor pictures from toxin diffusion follow the product's duration of action and tend to resolve as the pharmacological effect wears off. A motor deficit unrelated to the toxin, with sudden or progressive onset, calls for medical assessment without delay, because it may have other causes. If the picture resembles an acute neurological event, see suspected stroke in the office.

When to refer?

Referral is not an admission of error: it is a safety decision. Consider referring when there is:

• motor deficit that is not explained by the expected effect of the toxin;
• persistent neuropathic pain;
• numbness that does not improve over follow-up, according to your judgment;
• associated signs of vascular or infectious compromise;
• any diagnostic doubt that exceeds your competence.

The destination can be neurology, plastic surgery, oral and maxillofacial surgery or another specialty, depending on the case. The logic of referring with a report is in patient referral in HOF.

What to tell the patient?

Communication needs to be calm, objective and not minimizing. Avoid phrases such as "that's normal" before examining.

Information about the possibility, even if rare, of changes in sensation and movement should be in the informed consent. The medical history should also record prior neurological conditions, so the professional does not attribute to the procedure what was already there.

Review quiz

How does Harmy relate to this topic?

Harmy does not detect or simulate nerve injury. What it offers is communication and record support: marking of the areas, the ml per area and the front photos saved per patient in the history. For the clinical documentation of a complication, your office's patient record remains the source.

Prevention is the cheapest part of any approach: know the anatomy, use the right instrument, stop at atypical pain and inform the patient beforehand. When a complication occurs, the best response is a well-done exam, a complete record and a referral without delay.