Claudio Solaro, MD, Department of Neurology, ASL 3 Hospitals, Genoa, Italy

Introduction
Pain is defined as an 'unpleasant sensory experience associated with actual or potential tissue damage or described in terms of such damage'. Although symptom management in MS represents a primary focus for health care professionals, data available in the literature on pain management is lacking. Neurogenic pain common in MS includes dysesthetic pain, trigeminal neuralgia, painful tonic spasms and Lhermitte’s sign. Ethical issues regarding studies on pain make it difficult to identify the best treatment strategies based on comparisons of medication versus a placebo. Thus, for many of these symptoms treatment is based on anecdotal information and small, unblinded trials.

Dysesthetic pain
A number of studies have reported dysesthetic pain to be among the most common pain syndromes associated with MS. Dysesthetic pain is described as a constant symmetric or asymmetric burning sensation, usually affecting a person’s lower limbs, more frequently distally (meaning farther away from the body, such as in the feet and lower legs) than proximally (meaning closer to the body, such as in the upper part of the legs). A degree of sensory loss associated with dysesthetic pain can be detected during a neurological examination.
First-line medications for the treatment of dysesthetic pain in MS are tricyclic antidepressants, including amitriptyline, nortriptyline and clomipramine. Anticonvulsant medications such as carbamazepine, lamotrigine and gabapentin are also used in treating dysesthetic pain associated with MS. Carbamazepine appears to have a higher incidence of side effects, when compared to gabapentin and lamotrigine. Some people have difficulty tolerating this medication due to its side effects, and are not able to even reach the dose necessary for the mediation to be effective. It is not uncommon for a person to try different medications before finding one that is effective and tolerable.

Open communication with the neurologist is very important throughout this process. In general, anticonvulsant medications, as well as tricyclic antidepressants, may be useful in some MS patients, although unfortunately there is not enough data available from studies with large numbers of participants, which is necessary for drawing conclusions as to the best choice of medication.

Trigeminal neuralgia
Trigeminal neuralgia (TN) is probably the most widely recognised neurogenic pain syndrome in MS. It affects the trigeminal nerve, one of the largest nerves in the head. The trigeminal nerve sends impulses of touch, pain, pressure and temperature to the brain from the face, jaw, gums, forehead and around the eyes. TN in people with MS has been widely studied, with prevalence ranging from 1.9 percent to 4.4 percent. TN is characterised by paroxysmal (sudden), episodic facial pain which occurs in the area of the fifth cranial or trigeminus nerve, often triggered by touch, chewing, shaving or even a light breeze.
TN in MS and essential TN (TN not related to MS) differ in that TN in MS is more often bilateral (occurs on both sides of the face) and tends to occur at a younger age. Essential TN is most frequently caused by a blood vessel pressing on the nerve near the brain stem. Over time, changes in the blood vessels of the brain can result in a blood vessel rubbing against the trigeminal nerve root. The constant rubbing with each heartbeat wears away the insulating membrane of the nerve, resulting in nerve irritation.

TN in MS is likely to be caused by a plaque at the TN nerve entry zone in the nerve fibres on the lower front surface of the brain. However, magnetic resonance imaging (MRI) studies have demonstrated conflicting results, pointing to multiple causes of TN, even in the same person with MS. Treatment of TN primarily consists of anticonvulsant medications.
Some antidepressant drugs can also be helpful in relieving this type of pain.

Non-pharmacological interventions for trigeminal neuralgia
When medications are ineffective or if they produce undesirable side effects, neurosurgical procedures are available to relieve pressure on the nerve, to reduce nerve sensitivity or to interrupt the nerve pathway. These procedures have been reported as treatment for TN associated with MS, although with small numbers of people and limited follow-up. These techniques can cause nerve damage which may lead to increased sensitivity or numbness in the affected area, decreased corneal reflex, temporary difficulty chewing and hearing loss.

Painful tonic spasms
Painful tonic spasms (PTS) are described as a cramping, pulling pain and can affect both the upper and lower limbs, although they are more common in the lower extremities. The spasms are triggered by movements or sensory stimuli, often occurring during the night. PTS are estimated to occur in approximately 11 percent of people with MS.
PTS indirectly result from a lesion triggering the painful spasms in the central nervous system. Antispasticity medications, such as baclofen and benzodiazepines, gabapentin and tiagabine, are largely used for the treatment of PTS.

Trigeminal nerve