• Trigeminal Neuralgia-neuropathological mechanism and treatment strategies.

    27 September at 18:46 from atlas

    TRIGEMINAL NEURALGIA (TN) is also known as tic douloureux, prosopalgia or Fothergill's disease.It is a condition which is both under diagnosed, and misdiagnosed because of the nature of symptoms in the face ,and absence of headaches places it low on the differential diagnoses list.The symptoms are often dramatic and suggest dental or facial pathology unless the practitioner is aware of this unusual condition.it indeed has been poorly understood up until recent decades even amongst the Neuroscientific community.

    TN is characterised by episodes of sharp, lancinating,intense pain in one or more of the distributions of the trigeminal nerve in the face.TN often has triggers , which are germaine to the diagnosis, such as touching the face, a cold breeze on the face, shaving or a bed sheet brushing against the face at night.The potential for suspecting non-organic disease is obvious.In most case TN symptoms begin before age 50, although no age group is spared.

    It is a most unusual condition with a dramatic presentation with patients often terrified of opening the fridge at night with cold air on the face causing lancinating facial pain of intense levels.It can come in cycles with extended remissions, typical of many Neurological conditions .It is more common in women (2:1 to 4:3  F:M ratio) and it affects the right side of the face more frequently(about R:L 3:2).

    In many instances, the patients are investigated and treated for dental conditions,shingles,paranasal sinus disease or psychiatric conditions.Indeed, malignant skull base tumours can present with severe facial pain.

    In about 5-8 % of cases TN arises from a benign tumour in the cerebella-pontine angle such as a meningioma, epidermoid, or acoustic neuroma. In 2-3 % of cases it is due to multiple sclerosis, in the latter it tends to be bilateral.

    TN is due to cross compression of the trigeminal nerve at near its pontine  brain stem origin by usually an aberrant, ectatic vascular loop-usually of the superior cerebellar artery.Janetta described the now standard"Janetta's procedure' involving a suboccipital craniectomy, depressing the cerebellum inferiorly and medially and exposing the trigeminal nerve after coagulating bridging veins and dividing the arachnoid micro surgically.The loop is carefully microneurosurgically dissected away from the TN and a material such as synthetic sponge, teflon etc is placed to separate the nerve from the pulsating vessel.The success rate is of the order of 90-95% and the recurrence rate is 3-4% per annum.There are however significant risks including ataxia from cerebellar retraction, bleeding, meningitis (bacterial and chemical), facial numbness, deafness and facial paralysis.

    Treatment options include the above surgery , often referred to as 'MVD" (micro-vascular decompression),drugs such as tegretol, dilantin, lyrics, epilim, ended, baclofen etc-often with excellent long term results and good control with improved quality of life. Simple or opioid analgesics are rarely successful.

    Side-effects, failure or complications often lead the patient from the Neurologist to the Neurosurgeon for consideration of the more invasive, riskier but usually more successful treatments. These include: injection of chemicals such as glycerol into Meckel's cave through the side of the face(percuatneous glycerol trigeminal rhizolysis), balloon or radio frequency lesioning of the nerve again via a similar approach as the injection options.Gamma or Cyber knife radio surgery is gaining momentum as a treatment modality. These latter procedures whilst carrying less risk, tend to unfortunately have a higher and earlier recurrence rate.

    The patient with TN may well require a combination of treatments for this often chronic, relapsing and often disabling condition.The choice of treatment option will of course depend on the severity, chronicity, frequency of pain along with the patient's age and general medical status and expectations and consideration of 'benefit/ risk' ratio.Currently, most TN patients utilise medications such as Tegretol  and TCA or Lyrica along with Glycerol and sometimes a MVD.Investigations for TN include: CT, MR, MR Trigeminal neurography,MR cerebral angiography and careful neurologic and facial examination.

    Cyber or gamma knife radiosurgery is an exciting therapy being evaluated targetting the TN at its pontine origin.Availability is an issue with no such units in Queensland at this time.

    Patients MUST always seek and follow their own treating doctor's advice.

    ASSISTANT PROFESSOR MICHAEL CORONEOS CIME

    SENIOR BRISBANE NEUROSURGEON.