Cerebrospinal fluid (CSF) analysis is a basic tool for diagnosis of neurological diseases. Knowledge regarding blood–CSF barrier function (molecular flux/CSF flow theory) and neuroimmunology is reviewed to aid understanding and evaluation of CSF data. Intrathecal doses based on body surface area (i.e., 12 mg/m 2, maximum 15 mg) reported to result in low CSF methotrexate concentrations and reduced efficacy in pediatric patients. 262 Introduction. Multiple Sclerosis (MS) is a chronic inflammatory, demyelinating, and neurodegenerative disorder of the central nervous system (CNS) that affects the white and grey matter of the brain, spinal cord, and optic nerve. Back to Top A Abductor muscle. A muscle used to pull a body part away from the midline of the body (e.g., the abductor leg muscles are used to spread the legs). Multiple sclerosis (MS) is diagnosed on the basis of clinical findings and supporting evidence from ancillary tests, such as magnetic resonance imaging (MRI) of the brain and spinal cord and cerebrospinal fluid examination. Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease that affects the central nervous system (CNS). Several therapies for it exist, although there is no known cure. Methotrexate is contraindicated in pregnancy in women who are being treated for nonmalignant diseases (e.g., psoriasis, rheumatoid arthritis, polyarticular juvenile idiopathic arthritis). Methotrexate is contraindicated in pregnancy in women who are being treated for nonmalignant diseases (e.g., psoriasis, rheumatoid arthritis, polyarticular juvenile idiopathic arthritis). Multiple sclerosis (MS) is an immune-mediated inflammatory disease that attacks myelinated axons in the central nervous system, destroying the myelin and the axon in variable degrees and producing significant physical disability within 20–25 years in more than 30% of patients. Methotrexate is an antimetabolite of the antifolate type. It is thought to affect cancer and rheumatoid arthritis by two different pathways. For cancer, methotrexate competitively inhibits dihydrofolate reductase (DHFR), an enzyme that participates in the tetrahydrofolate synthesis.