E. Magnetic
resonance spectroscopy has shown that
patients with trigeminal neuropathy have a
significant reduction in the N-acetylaspartate
to creatine ratio, a biochemical marker of
neural viability, in the region of the thalamus
that also displays grey matter volume loss: but this is still experimental






Treating or “Managing” Neuropathic Pain 


As with all disease process, most eye surgeons and doctors prefer or should prefer to try natural remedies first. 


Natural compounds have been used in mild neuropathic pain with varying results. 
Here are some options that have been used:


1. Topical capsaicin cream
(0.025% and 0.075% capsaicin concentration; 
TGA indicated for the treatment of postherpetic
neuralgia).20 
The cream is applied for
five to 10 minutes twice daily for eight weeks
to the painful oral mucosa. The capsaicin
can cause an initial burning sensation in the
first few days; this can be reduced by pretreating
the mucosa with topical anaesthetic
mouthwash (lidocaine 1%).
There is some evidence for using 


2.Topical
ginger (containing gingerol) applied topically can work as antineuropathic.


3. Palmitoylethanolamide,
an active compound
from egg yolk and peanut oil, being effective
in the treatment of neuropathic pain.31


4. For nerve compression:
-acupuncture, massaging, physical therapy, electric heat massagers have been used to help. 


5. For Dry Eye Related Neuropathic pain:
-lid hygiene, warm compresses, non-preserved artificial tears, blinking exercises, lid massaging, high dose Omega 3, moisture chamber goggles, humidifier, anti-inflammatory diets, Lipiflow, Intense Pulse Light, Autologous Serum, Platelet Rich Plasma, –all try to noninvasively and naturally relieve pain. If these do not work or a patient does not mind using drugs, we try Xiidra, Restasis, Doxycycline pills, Punctal Plugs, Testosterone Cream, True Tear, Meibomian gland probing and expression, lid tarsorrhaphy if dryness is causing corneal abrasions or melts.


6. For chronic dental pain: a dental stent or mouth guard can be constructed by a dentist. 




Prescription Medicines for Neuropathic Pain:


1. First-line medicines:
1) Antidepressants: 
A. Tricyclic Antidepressants:
-can start with 25 mg for neuropathic pain: low doses ususally give less side effects, such as dry mouth, drowsiness, dry eye, weight gain.
If a patient is having terrible pain that he or she cannot sleep, we first get the pain under control before worrying about the worsening dry eye these medications can cause. It can be a Catch 22 with these medications but is important to find a non-narcotic to get rid of the pain to allow one to sleep. Lack of sleep or insomnia also worsens dry eye. 
a. Amitriptyline
b. Nortriptyline
c. Dothiepin


B. Selective serotonin and norepinephrine reuptake inhibitor (SNRI)
a. Duloxetine 
b. Venlafaxine




2) Anticonvulsants:
a. Gabapentin (aka GABA)
b. Pregabalin
c. Carbamazepine: this is used in  trigeminal neuralgia: another reported rare risk is below
d. Sodium valproate (aka oxcarbazepine: usually prescribed by neurologists): this is used off label for neuropathic pain


3) 5% lidocaine patches over pain area, such as in post herpetic neuralgia


2. Second-line medicines:
1) Opioids including tramadol and morphine: which we try to avoid at all costs as they are very addictive. 


3. Other: rarely used;
a. For eye pain:
Topical application of naltrexone hydrochloride (NTX), an opioid antagonist: has been used in Ref 3 below, but it is hard to get. 
Low Dose Naltrexone 1.5mg-4.5mg per day is sometimes used for Neuropathic Eye Pain, but side effects can limit effectiveness: side effects can include nightmares, insomnia, nausea. 


b. For other neuropathic pain: Mexiletine, a nonselective sodium channel blocker used for cardiac arrhythmias


b.  Stellate ganglion blocks with bupivacaine or guanethidine


For Severe Breakthrough Pain: Recommend hospitalization under the care of a pain clinic team for close supervision of use of IV opioids, antineuropathics and NMDA antagonists (ketamine).

Psychological and Behavioral
Management of Pain:
Psychological treatments are crucial for
many patients with chronic pain. Anxiety and depression is
common in patient struggling with chronic pain. Psychiatric diagnoses have been reported in
72% of patients with chronic pain conditions. The presence
of negative thoughts of anxiety, despair, depression increases pain intensity in patients
with acute postoperative pain.


Maintaining physical activity, social activities (especially with loved ones and friends), and even maintaining work schedules with its set order and plan of life likely helps prevent full focus on the chronic pain condition: though trying to limit electronic screen time or have more breaks is recommended.


Cognitive behavioral therapy can be helpful in pain rehabilitation.


Thus a recommended Overall Plan with treating chronic pain conditions could be:
1.  Explaining pain cause as best as possible
2. Try Natural treatments including prayer, meditation, relaxation, mindfulness
3. If natural options do not help, try Rx options under careful observation for side effects
4. Discuss and planned physical activity with pain specialist
5. Discuss psychological distress with PCP, MD, or pain specialist. 
6. Support restoration of social roles as best as can. 
7. Encourage active self-management
strategies to help wean
patients off medications over time.




Reference:
1. A.B. O’Connor, R.H. Dworkin

Dry eye reversal and corneal sensation restoration with topical naltrexone in diabetes mellitus.