Multiple Sclerosis (MS)
Multiple sclerosis is an autoimmune neurological disease characterized by the destruction of the myelin sheaths (nerve insulators) on neurons in the central nervous system. Its symptoms can vary, but eye pain, difficulty balancing, and numbness, tingling, and weakness in limbs are common. Attacks are “multiple” over time and/or location in the nervous system.
Multiple sclerosis (MS) is a neurodegenerative disease characterized by what is most likely an autoimmune attack on the central nervous system. The most well-known aspect of MS (and the reason for its name) is the destruction of the myelin sheaths that insulate neurons, which results in the formation of lesions throughout the brain and spinal cord. The myelin sheath forms the insulation around axons of neurons, and allows efficient propagation of electrical impulses from one neuron to the next. Their destruction slows down or stops electrical conduction, leading to the neurological deficits seen in the condition. 
The main symptoms of multiple sclerosis are optic neuritis, blurred or double vision, instability/dizziness, numbness or tingling in limbs, weakness in limbs muscle spasticity, incontinence. The main signs of multiple sclerosis are lesions in the central nervous system.
No single piece of information is sufficient for diagnosing MS. In order for a clinician to make an MS diagnosis, they must (a) observe lesions in ≥2 areas of the central nervous system and (b) find evidence that these lesions formed at different points in time. More details about the diagnosis of MS can be found here.
Drugs are the primary treatment for MS. Drugs are used to either (a) reduce the rate of disease progression or the rate of relapse; (b) manage relapses by speeding recovery; or (c) treat specific symptoms.
Vitamin D, vitamin A, biotin, and L-carnitine have all been studied for multiple sclerosis. Although all of them could potentially have effects on the disease (i.e., there are plausible mechanisms for them to improve MS), no research thus far has been tremendously compelling.
There hasn’t been much research on diet and MS, but it’s been hypothesized that hypercaloric and proinflammatory diets (like the Western diet) may be harmful for MS. Additionally, individuals who are obese (BMI≥30 kg/m2) in early life (childhood to young adulthood) have about double the risk of developing MS as individuals who are not obese (BMI<30 kg/m2) during this time period.
Cannabinoids can bind to receptors throughout the brain and body and play a role in motor control, inflammation, and cognition. So far, it seems that cannabis (or synthetic cannabinoids) can slightly reduce pain and bladder dysfunction, and many patients report improvements, but these outcomes can’t be measured objectively. It’s not clear if cannabis improves cognitive symptoms beyond any mood-elevating properties.
The immune system is heavily involved in the development of MS, but it’s not clear what provokes this response in the first place. Genetics, viral infections, and other environmental factors have all been connected to MS in observational research. Psychological stress (e.g., parental divorce and extreme grief) may also predispose people to the disease.