Methylnaltrexone (MNTX, brand name Relistor), used in form of methylnaltrexone bromide (INN, USAN, BAN), is a medication that acts as a peripherally acting μ-opioid receptor antagonist that acts to reverse some of the side effects of opioid drugs such as constipation without significantly affecting pain relief or precipitating withdrawals. Because MNTX is a quaternary ammonium cation, it cannot cross the blood–brain barrier, and so has antagonist effects throughout the body, counteracting effects such as itching and constipation, but without affecting opioid effects in the brain such as pain relief. However, since a significant fraction (up to 60%) of opioid analgesia can be mediated by opioid receptors on peripheral sensory neurons, particularly in inflammatory conditions such as arthritis, traumatic or surgical pain, MNTX may increase pain under such circumstances. Medical uses
Methylnaltrexone is approved for the treatment of opioid-induced constipation in chronic non cancer pain or when ordinary laxatives have failed. Mechanism of action
Methylnaltrexone is a peripheral acting mu-opioid receptor antagonist, and does not cross the blood brain barrier. Methylnaltrexone has restricted access through the blood brain barrier because it is a quaternary amine, which carries a positive charge when in a solution and more has polarity with lower lipid solubility than a lot of the opioid agonists used for pain treatment. The peripheral action of methylnaltrexone makes it effective for decreasing the constipating effects of opioids, without interfering with the analgesic effects (of opioids) on the central nervous system.
Thoracic spinal stenosis, at the level of the mid-back, is much less common.In lumbar stenosis, the spinal nerve roots in the lower back are compressed which can lead to symptoms of sciatica (tingling, weakness, or numbness that radiates from the low back and into the buttocks and legs).Cervical spinal stenosis can be far more dangerous by compressing the spinal cord. Cervical canal stenosis may lead to myelopathy, a serious condition causing symptoms including major body weakness and paralysis. Such severe spinal stenosis symptoms are virtually absent in  lumbar stenosis, however, as the spinal cord terminates at the top end of the adult lumbar spine, with only nerve roots (cauda equina) continuing further down. Cervical spinal stenosis is a condition involving narrowing of the spinal canal at the level of the neck. It is frequently due to chronic degeneration, but may also be congenital or traumatic. Treatment frequently is surgical. Signs and symptoms
Common
Standing discomfort (94%)
Discomfort/pain, in shoulder, arm, hand (78%)
Bilateral symptoms (68%)
Numbness at or below the level of involvement  (63%)
Weakness at or below the level of involvement  (43%)
Pain or weakness in buttock / thigh only (8%)
Pain or weakness below the knee (3%)

Neurological disorders
Cervical (spondylotic) myelopathy, a syndrome caused by compression of the cervical spinal cord which is associated with "numb and clumsy hands", imbalance,   loss of bladder and bowel control, and weakness that can progress to paralysis. Pinched nerve, causing numbness.