Anaesthesia Dolorosa

Anaesthesia dolorosa is severe, constant pain in an area of facial numbness, most often after destructive treatment of the trigeminal nerve (rhizotomy, thermocoagulation, glycerol injection, balloon compression, radiosurgery) or trauma, tumour or surgery involving the nerve. It affects a small proportion of patients (up to 1 to 4%) after ablative procedures for trigeminal neuralgia.

Pathophysiology. Deafferentation causes central sensitisation, spontaneous ectopic discharge from injured fibres and loss of inhibitory control in the trigeminal nucleus.

Constant burning, crushing, aching or tearing pain in a numb area of the face, with superimposed shocks, allodynia and dysaesthesia. Corneal anaesthesia places the eye at risk (keratitis, ulcer). Depression, sleep disturbance and suicidal thoughts are common.

Red flags.

• Corneal ulcer or visual loss in the numb eye.
• Depression, hopelessness or suicidal ideas.

Clinical diagnosis from a typical history of previous nerve injury or ablation, sensory loss and pain in the same distribution. MRI of the brain and trigeminal nerve to exclude tumour or recurrence. Assess depression and risk. Ophthalmology review for corneal sensation.

Differential diagnosis.

• Recurrent trigeminal neuralgia and painful post-traumatic trigeminal neuropathy.
• Persistent idiopathic facial pain and postherpetic neuralgia.
• Tumour of the skull base.

Prevention is key: avoid destructive procedures where microvascular decompression or other options are suitable.

Drugs. Amitriptyline 10 mg at night, increased to 75 mg, gabapentin 300 mg daily, increased to 1800 to 2400 mg daily in divided doses, pregabalin 75 to 300 mg twice daily (adjust to eGFR), duloxetine 60 mg daily, carbamazepine 100 mg twice daily, increased cautiously, or lamotrigine. Topical lidocaine or capsaicin. Opioids have limited value.

Neuromodulation. Motor cortex stimulation, deep brain stimulation, repetitive transcranial magnetic stimulation, or spinal trigeminal nucleus procedures (DREZ lesioning) in refractory cases.

Eye care. Lubricants, protective glasses and tarsorrhaphy for corneal anaesthesia.

Psychology. Cognitive behavioural therapy, pain management programmes and mood treatment. Assess suicide risk and arrange urgent support if needed.

Monitoring. Pain, mood and corneal health.

Referral and escalation. Refer to pain services, neurosurgery, ophthalmology and psychiatry.