Lectures: Laboratory Findings
It is important to remember that no laboratory test is specifically diagnostic for MS. However, a number of studies can be helpful to confirm a suspected diagnosis of MS and help separate demyelinating lesions in time and space.
Cerebral Spinal Fluid Studies
Cerebral spinal fluid studies can confirm demyelinating disease of the nervous system. They show an increase in immunoglobulin concentrations in more than 90% of patients with MS. IgG index (a comparison between IgG levels in the CSF and in the serum) is elevated in many MS patients. Oligoclonal Immunoglobulin Bands can be identified in the CSF of MS patients via electrophoresis. The overall protein level is also slightly elevated - up to 0.1 g/L. Protein level can be higher if the patient is going through a marked relapse (i.e.,. severe optic neuritis). Some patients also exhibit a slight elevation in cell count (up to 50 per cubic millimeter ). Most cells can be identified as T-lymphocytes.Oligoclonal Bands in CSF
Evoked Potentials Studies
Evoked potentials studies can be helpful in providing evidence of separation of lesions in space. An abnormal slowing of electrical impulses is used to assess this separation. The most commonly used evoked potentials in patients with MS are Visual Evoked Responses (VER), Brain stem Auditory Evoked Responses (BAER), and Somatosensory Evoked Responses (SSER). Approximately 75% of MS patients exhibit abnormal VER regardless of whether a patient does or does not have a history of clinically apparent optic neuritis. In a latter case, abnormal visual evoked response can be used to identify a para clinical second lesion and confirm the diagnosis of MS. The BAER is harder to interpret and only 30% of patients exhibit abnormal response from the central hearing areas in the brain stem. The SSEP is technically the most challenging study to perform, but is found to be abnormal in more than 80% of patients with definite MS. This study can help identify slowed conduction in the central sensory pathways, and help distinguish peripheral lesions from central ones.Visual Evoked Potentials
Magnetic Resonance Imaging
Magnetic Resonance Imaging is important in both confirming the diagnosis of MS and understanding the dynamics of demyelinating plaques development in patients with MS. However, it is important to understand that abnormal MRI findings without clinical evidence are not sufficient to confirm a diagnosis of MS. Conversely, an absence of abnormal MRI findings in clinically definite MS does not disprove the diagnosis.
On T-2 weighted images, patchy areas of abnormal white matter are found most commonly in cerebral hemispheres in paraventricular areas;
Often, lesions can be present in the cerebellum and brain stem;
Lesions can be present in cervical and/or thoracic spinal cord;
Gadolinium enhancement on the MRI scan is considered a sign of an active lesion, but it does not necessarily correlate with increased disease activity.
Abnormal MRI scans are found in:
- 90% of patients with definite diagnosis of MS;
- 70% of patients with diagnosis of probable MS;
- 30%-50% of patients with possible MS;
There are three criteria for the MRI diagnosis of MS (Fazekas et al.):
- Lesions abutting the lateral ventricles
- Lesions with diameter greater than 0.6 cm
- Lesions present in the posterior fossa
(Use with caution in patients with other diseases that can affect MRI results, see Differential Diagnosis chapter of this program.)
There is a poor correlation between the size and area of lesions present on MRI images and the patient's disability, i.e.,. Patients with large lesions may have minor clinical findings, and patients with small lesions may have severe disability. However, increase in the area and number of lesions in the cerebral hemispheres or the thinning of corpus callosum may correlate with poor cognitive function in patients.
Presence of lesions in the spinal cord does not correlate with disease severity. Presence of spinal cord atrophy does correlate with greater disability.
Cerebral Spinal Fluid Studies: MRI Scans:
Blood and Urine Tests
Blood and urine tests are nonspecific and unremarkable in patients with MS. Attempts are currently under way to develop quantitative techniques to assess Myelin breakdown products excreted in urine in MS patients. No clinical applications of this technique are available yet. Blood may need to be monitored in patients who take medications with liver toxicity side effects, anticonvulsant medications, immunosuppressants, etc. Urine studies are done when a patient has symptoms of urinary tract infection, or if a patient is taking a medication with known nephrotoxicity.