AQP4-Ab-negative NMO presents problems for diagnosis. The behavior of the oligoclonal bands respect MS can help to establish a more accurate diagnosis. Oligoclonal bands in NMO are rare and they tend to disappear after the attacks, while in MS they are nearly always present and persistent.

It is important to notice for differential diagnosis that, though uncommon, it is possible to have longitudinal lesions in MS

Other problem for diagnosis is that AQP4ab in MOGab levels can be too low to be detected. Some additional biomarkers have been proposed.

The Mayo Clinic proposed a revised set of criteria for diagnosis of Devic's disease in 2006. Those new guidelines require two absolute criteria plus at least two of three supportive criteria. In 2015 a new review was published by an international panel refining the previous clinical case definition but leaving the main criteria unmodified:

Absolute criteria:

1. Optic neuritis

2. Acute myelitis

Supportive criteria:

1. Brain MRI not meeting criteria for MS at disease onset

2. Spinal cord MRI with continuous T2-weighted signal abnormality extending over three or more vertebral segments, indicating a relatively large lesion in the spinal cord

3. NMO-IgG seropositive status (The NMO-IgG test checks the existence of antibodies against the aquaporin 4 antigen.)

Myelitis has an extensive differential diagnosis. The type of onset (acute versus subacute/chronic) along with associated symptoms such as the presence of pain, constitutional symptoms that encompass fever, malaise, weight loss or a cutaneous rash may help identify the cause of myelitis. In order to establish a diagnosis of myelitis, one has to localize the spinal cord level, and exclude cerebral and neuromuscular diseases. Also a detailed medical history, a careful neurologic examination, and imaging studies using magnetic resonance imaging (MRI) are needed. In respect to the cause of the process, further work-up would help identify the cause and guide treatment. Full spine MRI is warranted, especially with acute onset myelitis, to evaluate for structural lesions that may require surgical intervention, or disseminated disease. Adding gadolinium further increases diagnostic sensitivity. A brain MRI may be needed to identify the extent of central nervous system (CNS) involvement. Lumbar puncture is important for the diagnosis of acute myelitis when a tumoral process, inflammatory or infectious cause are suspected, or the MRI is normal or non-specific. Complementary blood tests are also of value in establishing a firm diagnosis. Rarely, a biopsy of a mass lesion may become necessary when the cause is uncertain. However, in 15–30% of people with subacute or chronic myelitis, a clear cause is never uncovered.

Below are various methods/techniques used to diagnose demyelinating diseases.

- Exclusion of other conditions that have overlapping symptoms

- Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to visualize internal structures of the body in detail. MRI makes use of the property of nuclear magnetic resonance (NMR) to image nuclei of atoms inside the body. This method is reliable because MRIs assess changes in proton density. "Spots" can occur as a result of changes in brain water content.

- Evoked potential is an electrical potential recorded from the nervous system following the presentation of a stimulus as detected by electroencephalography (EEG), electromyography (EMG), or other electrophysiological recording method.

- Cerebrospinal fluid analysis (CSF) can be extremely beneficial in the diagnosis of central nervous system infections. A CSF culture examination may yield the microorganism that caused the infection.

- Quantitative proton magnetic resonance spectroscopy (MRS) is a non-invasive analytical technique that has been used to study metabolic changes in brain tumors, strokes, seizure disorders, Alzheimer's disease, depression and other diseases affecting the brain. It has also been used to study the metabolism of other organs such as muscles.

- Diagnostic criteria refers to a specific combination of signs, symptoms, and test results that the clinician uses in an attempt to determine the correct diagnosis.

- Fluid-attenuated inversion recovery (FLAIR) uses a pulse sequence to suppress cerebrospinal fluid and show lesions more clearly, and is used for example in multiple sclerosis evaluation.

For diagnosis of NPSLE, it must be determined whether neuropsychiatric symptoms are indeed caused by SLE, whether they constitute a separate comorbid condition, or whether they are an adverse effect of disease treatment. In addition, onset of neuropsychiatric symptoms may happen prior to the diagnosis of lupus. Due to the lack of uniform diagnostic standards, statistics about NPSLE vary widely.

Tests which aid in diagnosis include MRI, electrophysiological studies, psychiatric evaluation, and autoantibody tests.

As in multiple sclerosis, another demyelinating condition, it is not possible to predict with certainty how CIDP will affect patients over time. The pattern of relapses and remissions varies greatly with each patient. A period of relapse can be very disturbing, but many patients make significant recoveries.

If diagnosed early, initiation of early treatment to prevent loss of nerve axons is recommended. However, many individuals are left with residual numbness, weakness, tremors, fatigue and other symptoms which can lead to long-term morbidity and diminished quality of life.

It is important to build a good relationship with doctors, both primary care and specialist. Because of the rarity of the illness, many doctors will not have encountered it before. Each case of CIDP is different, and relapses, if they occur, may bring new symptoms and problems. Because of the variability in severity and progression of the disease, doctors will not be able to give a definite prognosis. A period of experimentation with different treatment regimens is likely to be necessary in order to discover the most appropriate treatment regimen for a given patient.

There are several types of immune-mediated neuropathies recognised. These include

- Chronic inflammatory demyelinating polyneuropathy (CIPD) with subtypes:

- Classical CIDP

- CIDP with diabetes

- CIDP/monoclonal gammopathy of undetermined significance

- Sensory CIDP

- Multifocal motor neuropathy

- Multifocal acquired demyelinating sensory and motor neuropathy (Lewis-Sumner syndrome)

- Multifocal acquired sensory and motor neuropathy

- Distal acquired demyelinating sensory neuropathy

- Guillain-Barre syndrome with subtypes:

- Acute inflammatory demyelinating polyradiculoneuropathy

- Acute motor axonal neuropathy

- Acute motor and sensory axonal neuropathy

- Acute pandysautonomia

- Miller Fisher syndrome

- IgM monoclonal gammopathies with subtypes:

- Waldenstrom's macroglobulinemia

- Mixed cryoglobulinemia, gait ataxia, late-onset polyneuropathy syndrome

- Myelin-associated glycoprotein-associated gammopathy, polyneuropathy, organomegaly, endocrinopathy, M-protein and skin changes syndrome (POEMS)

For this reason a diagnosis of chronic inflammatory demyelinating polyneuropathy needs further investigations.

The diagnosis is usually provisionally made through a clinical neurological examination. Patients usually present with a history of weakness, numbness, tingling, pain and difficulty in walking. They may additionally present with fainting spells while standing up or burning pain in extremities. Some patients may have sudden onset of back pain or neck pain radiating down the extremities, usually diagnosed as radicular pain. These symptoms are usually progressive and may be intermittent.

Autonomic system dysfunction can occur; in such a case, the patient would complain of orthostatic dizziness, problems breathing, eye, bowel, bladder and cardiac problems. The patient may also present with a single cranial nerve or peripheral nerve dysfunction.

On examination the patients may have weakness, and loss of deep tendon reflexes (rarely increased or normal). There may be atrophy (shrinkage) of muscles, fasciculations (twitching) and loss of sensation. Patients may have multi-focal motor neuropathy, as they have no sensory loss.

Most experts consider the necessary duration of symptoms to be greater than 8 weeks for the diagnosis of CIDP to be made.

Typical diagnostic tests include:

- Electrodiagnostics – electromyography (EMG) and nerve conduction study (NCS). In usual CIDP, the nerve conduction studies show demyelination. These findings include:

1. a reduction in nerve conduction velocities;

2. the presence of conduction block or abnormal temporal dispersion in at least one motor nerve;

3. prolonged distal latencies in at least two nerves;

4. absent F waves or prolonged minimum F wave latencies in at least two motor nerves. (In some case EMG/NCV can be normal).

- Serum test to exclude other autoimmune diseases.

- Lumbar puncture and serum test for anti-ganglioside antibodies. These antibodies are present in the branch of CIDP diseases comprised by anti-GM1, anti-GD1a, and anti-GQ1b.

- Sural nerve biopsy; biopsy is considered for those patients in whom the diagnosis is not completely clear, when other causes of neuropathy (e.g., hereditary, vasculitic) cannot be excluded, or when profound axonal involvement is observed on EMG.

- Ultrasound of the periferal nerves may show swelling of the affected nerves

- MRI can also be used in the diagnosic workup

In some cases electrophysiological studies fail to show any evidence of demyelination. Though conventional electrophysiological diagnostic criteria are not met, the patient may still respond to immunomodulatory treatments. In such cases, presence of clinical characteristics suggestive of CIDP are critical, justifying full investigations, including sural nerve biopsy.

Demyelinating diseases can be divided in those affecting the central nervous system and those presents in the peripheral nervous system, presenting different demyelination conditions. They can also be divided by other criteria in inflammatory and non-inflammatory, according to the presence or lack of inflammation, and finally, a division can also be made depending on the underlying reason for demyelination in myelinoclastic (myelin is attacked by an external substance) and leukodystrophic (myelin degenerates without attacks)

Management of neuropsychiatric lupus is similar to the management of neuropsychiatric disease in patients without lupus. Treatment depends on the underlying causes of a patient’s disease, and may include immunosuppressants, anticoagulants, and symptomatic therapy.

Since each case is different, the following are possible treatments that patients might receive in the management of myelitis.

- Intravenous steroids

High-dose intravenous methyl-prednisolone for 3–5 days is considered as a standard of care for patients suspected to have acute myelitis, unless there are compelling reasons otherwise. The decision to offer continued steroids or add a new treatment is often based on the clinical course and MRI appearance at the end of 5 days of steroids.

- Plasma exchange (PLEX)

Patients with moderate to aggressive forms of disease who don’t show much improvement after being treated with intravenous and oral steroids will be treated with PLEX. Retrospective studies of patients with TM treated with IV steroids followed by PLEX showed a positive outcome. It also has been shown to be effective with other autoimmune or inflammatory central nervous system disorders. Particular benefit has been shown with patients who are in the acute or subacute stage of the myelitis showing active inflammation on MRI. However, because of the risks implied by the lumbar puncture procedure, this intervention is determined by the treating physician on a case-by-case basis.

- Immunosuppressants/Immunomodulatory agents

Myelitis with no definite cause seldom recurs, but for others, myelitis may be a manifestation of other diseases that are mentioned above. In these cases, ongoing treatment with medications that modulate or suppress the immune system may be necessary. Sometimes there is no specific treatment. Either way, aggressive rehabilitation and long-term symptom management are an integral part of the healthcare plan.

In terms of the differential diagnosis for polyneuropathy one must look at the following:

Cerebrospinal fluid (CSF) analysis shows a large number of white blood cells. Typically small mature lymphocytes are the majority of cells seen, with monocytes and neutrophils making up the rest. Definitive diagnosis is based on histopathology, either a brain biopsy or post-mortem evaluation (necropsy). A CT scan or MRI will show patchy, diffuse, or multifocal lesions. For a number of years, the basic treatment was some type of corticosteroid in combination with one or more immunosuppressive drugs, typically cytosine arabinoside and/or cyclosporine or other medications such as azathioprine, cyclophosphamide, or procarbazine, of which were usually added one at a time to the corticosteroid until a successful combination was found. There is evidence that treatment with radiation therapy for focal GME provides the longest periods of remission.

CNS demyelinating autoimmune diseases are autoimmune diseases which primarily affect the central nervous system.

Examples include:

- Diffuse cerebral sclerosis of Schilder

- Acute disseminated encephalomyelitis

- Acute hemorrhagic leukoencephalitis

- Multiple sclerosis (though the cause is unknown, it is sure that immune system is involved)

- Transverse myelitis

- Neuromyelitis optica

Currently, the commonly accepted international standard for the clinical case definition is the one published by the International Pediatric MS Study Group, revision 2007.

The diagnosis of polyneuropathies begins with a history and physical examination to ascertain the pattern of the disease process (such as-arms, legs, distal, proximal) if they fluctuate, and what deficits and pain are involved. If pain is a factor, determining where and how long the pain has been present is important, one also needs to know what disorders are present within the family and what diseases the person may have. Although diseases often are suggested by the physical examination and history alone, tests that may be employed include: electrodiagnostic testing, serum protein electrophoresis, nerve conduction studies, urinalysis, serum creatine kinase (CK) and antibody testing (nerve biopsy is sometimes done).

Other tests may be used, especially tests for specific disorders associated with polyneuropathies, quality measures have been developed to diagnose patients with distal symmetrical polyneuropathy (DSP).

Also inside standard MS different clinical courses can be separated.

Some NMO patients present double positive for autoantibodies to AQP4 and MOG. These patients have MS-like brain lesions, multifocal spine lesions and retinal and optic nerves atrophy.

One third up to one half of people with PML die in the first few months following diagnosis, depending on the severity of their underlying disease. Survivors can be left with variable degrees of neurological disability.

Diagnosis of tumefactive MS is commonly carried out using magnetic resonance imaging (MRI) and proton MR spectroscopy (H-MRS). Diagnosis is difficult as tumefactive MS may mimic the clinical and MRI characteristics of a glioma or a cerebral abscess. However, as compared to tumors and abscesses, tumefactive lesions have an open-ring enhancement as opposed to a complete ring enhancement. Even with this information, multiple imaging technologies have to be used together with biochemical tests for accurate diagnosis of tumefactive MS.

Tumefactive demyelination is distinguished from tumor by the presence of multiple lesions, absence of cortical involvement, and decrease in lesion size or detection of new lesions on serial imaging

It took its name from Otto Marburg. It can be diagnosed "in vivo" with an MRI scan.

If Marburg disease occurs in the form of a single large lesion, it can be radiologically indistinguishable from a brain tumor or abscess. It is usually lethal, but it has been found to be responsive to Mitoxantrone and Alemtuzumab, and it has also been responsive to autologous stem cell transplantation. Recent evidence shows that Marburg's presents a heterogeneous response to medication, as does standard MS.

Lupus is a condition with no known cure. Lupus cerebritis however is treated by suppressing the autoimmune activity.

When it is caused by infections, treatment consists of medication that will primarily cure the infection. For inflammation, steroids can be used to bring down the swelling. If the swelling appears to have increased to a dangerous level, surgery may be needed to relieve pressure on the brain. The formation of an abscess also calls for surgery as it will be necessary to drain the abscess.

There is no specific pathological testing or technique available for the diagnosis of the disease, although the International Study Group criteria for the disease are highly sensitive and specific, involving clinical criteria and a pathergy test. Behçet's disease has a high degree of resemblance to diseases that cause mucocutaneous lesions such as "Herpes simplex" labialis, and therefore clinical suspicion should be maintained until all the common causes of oral lesions are ruled out from the differential diagnosis.

Visual acuity, or color vision loss with concurrent mucocutaneous lesions or systemic Behçet's disease symptoms should raise suspicion of optic nerve involvement in Behçet's disease and prompt a work-up for Behçet's disease if not previously diagnosed in addition to an ocular work-up. Diagnosis of Behçet's disease is based on clinical findings including oral and genital ulcers, skin lesions such as erythema nodosum, acne, or folliculitis, ocular inflammatory findings and a pathergy reaction. Inflammatory markers such ESR, and CRP may be elevated. A complete ophthalmic examination may include a slit lamp examination, optical coherence tomography to detect nerve loss, visual field examinations, fundoscopic examination to assess optic disc atrophy and retinal disease, fundoscopic angiography, and visual evoked potentials, which may demonstrate increased latency. Optic nerve enhancement may be identified on Magnetic Resonance Imaging (MRI) in some patients with acute optic neuropathy. However, a normal study does not rule out optic neuropathy. Cerebrospinal fluid (CSF) analysis may demonstrate elevated protein level with or without pleocytosis. Imaging including angiography may be indicated to identify dural venous sinus thrombosis as a cause of intracranial hypertension and optic atrophy.

The Poser criteria for diagnosis are:

- One or two roughly symmetrical large plaques. Plaques are greater than 2 cm diameter.

- No other lesions are present and there are no abnormalities of the peripheral nervous system.

- Results of adrenal function studies and serum very long chain fatty acids are normal.

- Pathological analysis is consistent with subacute or chronic myelinoclastic diffuse sclerosis.

PML is diagnosed in a patient with a progressive course of the disease, finding JC virus DNA in spinal fluid together with consistent white matter lesions on brain magnetic resonance imaging (MRI); alternatively, a brain biopsy is diagnostic when the typical histopathology of demyelination, bizarre astrocytes, and enlarged oligodendroglial nuclei are present, coupled with techniques showing the presence of JC virus.

Characteristic evidence of PML on brain CT scan images are multifocal, non-contrast enhancing hypodense lesions without mass effect, but MRI is far more sensitive than CT. The most common area of involvement is the cortical white matter of frontal and parieto- occipital lobes, but lesions may occur anywhere in the brain, like the basal ganglia, external capsule, and posterior cranial fossa structures like the brainstem and cerebellum.

Although typically multifocal, natalizumab-associated PML is often monofocal, predominantly in the frontal lobe.

Recently it has been found that CSF from MS patients can carry the disease to rodents, opening the door to an alternative model.