Multiple Sclerosis - Diagnosis and differential diagnosis

Frederik Barkhof, Robin Smithuis and Marieke Hazewinkel

From the MR Center for MS Research, Radiology Department of the 'Vrije Universiteit' Medical Center, Amsterdam and the Rijnland Hospital, Leiderdorp, the Netherlands


This review is based on a presentation given by FrederikBarkhof at the Neuroradiology teaching course for the Dutch Radiology Society and was adapted for the Radiology Assistant by Robin Smithuis and Marieke Hazewinkel.

This presentation will focus on the role of MRI in the diagnosis of Multiple Sclerosis.

We will discuss the following subjects:

  • Typical findings in MS
  • Role of MR in the McDonald criteria of MS
  • How to differentiate MS lesions from other white matter diseases
  • The importance of the a priori chance for the differential diagnosis of white matter lesions.


Multiple white matter lesions. MS or vascular?

One of the most common questions in daily radiology practice when we see an image like the one on the left is:

  • 'Do we have to think of Multiple Sclerosis?
  • Or are these white matter lesions the result of small vessel disease, as in a hypertensive patient?
  • Or should we think of more uncommon diseases?

In order to be able to answer that question, we have to realise that when we study white matter lesions (WMLs):

  1. Many neurological diseases can mimic MS both clinically and radiologically.
  2. Most incidentally found WMLs will have a vascular origin.
  3. The list of possible diagnoses of WMLs is long.

Multiple sclerosis

Typical MRI findings in MS

Multiple sclerosis (MS) is the most common inflammatory demyelinating disease of the central nervous system in young and middle-age adults, but also affects older people.
According to the McDonald criteria for MS, the diagnosis requires objective evidence of lesions disseminated in time and space.
As a consequence there is an important role for MRI in the diagnosis of MS, since MRI can show multiple lesions (dissemination in space), some of which can be clinically occult, and MRI can show new lesions on follow up scans (dissemination in time).

MS has a typical distribution of WMLs.
This can be very helpful in differentiating them from vascular lesions (see Table).
Typical for MS is involvement of corpus callosum, U-fibers, temporal lobes, brainstem, cerebellum and spinal cord.
This pattern of involvement is uncommon in other diseases.
In small vessel disease there may be involvement of the brainstem, but it is usually symmetrical and central, while in MS it is peripheral.

Here we see typical differences in vascular brainstem lesions compared to MS.

The image on the left is an axial T2 weighted image illustrating typical vascular brainstem involvement, with a central involvement of the transverse pontine fibers.

The image on the right is an axial T2 weighted image of the brainstem of an MS-patient, showing typical peripherally located white matter lesions, often in or near the trigeminal tract, or bordering the 4th ventricle.

Coronal PD image of a brain specimen with MS involvement

Even when a patient is clinically suspected of MS, we still have to study the WMLs carefully to decide whether these lesions are indeed suggestive of MS, and not incidental age-related findings.
We will discuss this more in detail when we look at the MRI criteria in the McDonald criteria for MS.

Here we have a coronal PD image of a brain specimen with MS involvement.
First look at the image and look for lesions that are specific for MS.
Than continue.

Coronal PD image of a brain specimen with MS involvement

The lesions in the deep white matter (yellow arrow) are nonspecific and can be seen in many diseases.

Typical for MS in this case is:

  • Involvement of the temporal lobe (red arrow)
  • Juxtacortical lesions (green arrow) - touching the cortex
  • Involvement of the corpus callosum (blue arrow)
  • Periventricular lesions - touching the ventricles
LEFT: involvement of U-fibers in MS. RIGHT: U-fibers are not involved in patient with hypertension.

Juxtacortical lesions are specific for MS.
These are adjacent to the cortex and must touch the cortex.
Do not use the word subcortical to describe this location, because that is a less specific term, indicating a larger area of white matter almost reaching the ventricles.
In small vessel disease these juxtacortical U-fibers are not involved and on T2 and FLAIR there will be a dark band between the WML and the (also bright) cortex (yellow arrow).

Temporal lobe involvement is also specific for MS.
In hypertensive encephalopathy, the WMLs are located in the frontal and parietal lobes, uncommonly in the occipital lobes and not in the temporal lobes.
Only in CADASIL there is early involvement of the temporal lobes.

Multiple WMLs with a typical distribution for MS.

First look at the images on the left.
Describe the lesions and decide which findings are typical for MS.

Typical findings for MS as seen in this case are:

  • Multiple lesions adjacent to the ventricles (red arrow).
  • Ovoid lesions perpendicular to the ventricles (yellow arrow).
  • Multiple lesions in brainstem and cerebellum.

These ovoid lesions are also called Dawson fingers.
They represent areas of demyelination along the small cerebral veins that run perpendicular to the ventricles.

SE PDW-image of the spinal cord in a patient with MS

First look at the spinal cord images on the left
Describe the lesions and decide which findings are typical for MS.

There are multiple lesions in the spinal cord. This is another typical feature of MS.
Typical spinal cord lesions in MS are relatively small and peripherally located.
They are most often found in the cervical cord and are usually less than 2 vertebral segments in length.

By the way did you notice the lesion in the brainstem?
A spinal cord lesion together with a lesion in the cerebellum or brainstem is very suggestive of MS.
Spinal cord lesions are uncommon in most other CNS diseases, with the exception of ADEM, sarcoid, Lyme disease and SLE.

Notice that this image is a proton density weighted image (PDWI).
They are crucial for studying the spinal cord.

On PDW-images the spinal cord has a uniformly low signal intensity (like CSF), which gives the MS lesions a good contrast against the surrounding CSF and normal cord tissue.
Use a 512 matrix and cardiac gating for optimal results.

LEFT: Typical Dawson finger with enhancement on T1WI. RIGHT: Multiple lesions and edema around enhancing lesion on T2WI.

Dawson fingers

First look at the images on the left
Describe the lesions and decide which findings are typical for MS.

Typical findings for MS as seen in this case are:

  • Ovoid lesions perpendicular to the ventricles (Dawson fingers).
  • Enhancing lesion.
  • Multiple lesions adjacent to the ventricles.

Dawson fingers are typical for MS and are the result of inflammation around penetrating venules.
These veins are perpendicular to the ventricular surface.

Enhancement is another typical finding in MS.
This enhancement will be present for about one month after the occurrence of a lesion.
The simultaneous demonstration of enhancing and non-enhancing lesions in MS is the radiological counterpart of the clinical dissemination in time and space.
The edema will regress and finally only the center will remain as a hyperintense lesion on T2WI.

Lymphocytic infiltration is seen surrounding a small vein. These lymphocytes attack the myeline.

On the left a specimen showing the perivenular inflammation in MS.
MS starts as inflammation around these veins.
In the first four weeks of the inflammation there is enhancement with gadolinium due to local interruption of the blood brain barrier.
First there is homogeneous enhancement but this can change to open ring enhancement.

Juxtacortical MS lesion located in the U-fiber.

Juxtacortical lesions located in the U-fibers are also very specific for MS.
You really have to look hard to notice them, because they are difficult to differentiate from the hyperintense cortex.
This patien not only has multiple periventricular lesions of which some have the typical Dawson finger aspect (blue arrow), but there is also a juxtacortical lesion.
The involvement of the U-fibers is best seen on the magnification view.

T1WI: multiple enhancing lesions

On the left a patient who was re-examined 3 months after the first clinical attack.
Describe the lesions and decide which findings are typical for MS.

Typical findings for MS as seen in this case are:

  • Multiple enhancing lesions
  • Many of these lesions 'touch the cortex' and must be located in the U-fibers.
  • These enhancing lesions all are new lesions, since Gadolinium enhancement is only visible for about 1 month.
    So this finding is proof of dissemination in time.
LEFT: Single lesion on T2WI.RIGHT: Two new lesions at 3 month follow-up.

New lesions on T2W images also indicate dissemination in time.
The patient on the left had a follow-up examination 3 months after the first clinical event.

Notice how similar the positioning is.
This allows good comparison of the images.
Optimal positioning is discussed in the MRI protocol (see later).

MS Variants and Differential diagnosis

Tumefactive MS. Arrow indicates biopsy site.

Tumefactive MS

Tumefactive MS is a variant of Multiple Sclerosis.
It on MRI presents as a large intra-parenchymal lesion with usually less mass effect than would be expected for its size.

After the administration of gadolinium, there may be some peripheral enhancement, often with an incomplete ring.
These lesions can be distinguished from gliomas or intraparenchymal abscesses, which typically have a closed-ring enhancement.

These T2W and T1W post-gadolinium images are of a 39 year old male who presented with subacute onset of hemianopsia.
He was referred for biopsy to differentiate between a glioma or demyelination.
There is an intraparenchymal mass in the right temporal and occipital lobe with a hypointense rim on T2, which only partially enhances (open-ring sign) on the postcontrast images.
There is surrounding edema, but relatively little mass effect.
This was a biopsy-proven demyelinating lesion.

The open-ring enhancement pattern with low signal T2 ring and low CBF are all indicative of demyelination.

Balo's Concentric Sclerosis

Balo's Concentric Sclerosis is an uncommon demyelinating disease.
It is characterized by alternative bands of demyelination and myelin preservation, often in whorl-like configurations.

Here T2 and postcontrast T1W images showing a large lesion in the left hemisphere with alternating T2-hyperintense and isointense bands.
On the T1W images after gadolinium there is alternating linear enhancement.
There is a smaller, similar lesion on the right.

Neuromyelitis Optica

A very important differential to keep in mind, especially in patients with a bilateral optic neuritis, is Neuromyelitis Optica (NMO) or Devic's Disease.
This is a demyelinating disease in which the optic nerves and spinal cord are usually involved.
Often there are few T2-lesions in the brain.
Think of NMO when there are extensive spinal cord lesions (more than 3 vertebral segments) with low T1-signalintensity and swelling of the cord.
On axial images the lesions often involve most of the cord.
This is unlike MS, in which the lesions are usually smaller and peripherally located.

Here we see a sagittal T2-weighted image of the spinal cord in a patient with NMO showing a longitudinally extensive cord lesion with marked swelling.
The clue to the diagnosis was the AQP4-AB titer 1:1024.

Read more on NMO in the spinal cord...

ADEM – extensive involvement of the cortical and gray matter - including thalamus.


Acute Disseminated Encephalomyelitis (ADEM)is another important differential diagnosis of MS.
This is a monophasic, immune-mediated demyelinating disease which often presents in children following an infection or vaccination.
On MRI there are often diffuse and relatively symmetrical lesions in the supra-and infratentorial white matter which may enhance simultaneously.
There almost always is preferential involvement of the cortical gray matter and the deep gray matter of the basal ganglia and thalami.

Here we have axial FLAIR and T2W-images of a young patient with ADEM - notice the extensive involvement of the cortical and gray matter, including thalamus.

Here another case of ADEM.

Notice the involvement of the basal ganglia.

Here another case of ADEM.

Notice the similarity to the other two cases.

McDonald criteria for MS

The diagnosis of MS requires elimination of more likely diagnoses and demonstration of dissemination of lesions in space and time.

Dissemination in Space (DIS) is:

  • ≥ 1 T2 lesion in at least two out of four areas of the CNS: periventricular, juxtacortical, infratentorial, or spinal cord
  • Gadolinium enhancement of lesions is not required for DIS

Dissemination in Time is:

  • A new T2 and/or gadolinium-enhancing lesion(s) on follow-up MRI, with reference to a baseline scan, irrespective of the timing of the baseline MRI OR
  • Simultaneous presence of asymptomatic gadolinium-enhancing and non-enhancing lesions at any time
Lesions refers to clinically detectable CNS-lesions.

The McDonald criteria for MS were recommended in 2001 by an international panel and revised in 2005 and 2010.

An Attack is:

  • Neurological disturbance of kind seen in MS
  • Subjective report or objective observation
  • At least 24 hours duration in absence of fever or infection
  • Excludes pseudoattacks, single paroxysmal symptoms (multiple episodes of paroxysmal symptoms occurring over 24 hours or more are acceptable as evidence)
  • Some historical events with symptoms and pattern typical for MS can provide reasonable evidence of previous demyelinating events, even in the absence of objective findings

Time Between Attacks:

  • 30 days between onset of event 1 and onset of event 2

Positive CSF is:

  • Oligoclonal IgG bands in CSF (and not serum) or elevated IgG index

The diagnosis is either:

  • MS : all criteria fulfilled
  • possible MS : not all criteria fulfilled
  • not MS : no criteria fulfilled

The McDonald criteria make use of the clinical presentation and the advances of MR imaging.
When a patient presents with 2 or more attacks with clinical evidence of 2 or more neurological deficits, there is no need for additional requirements to make the diagnosis of MS, because there is dissemination in place and time.

In all other cases (less than 2 attacks or less than 2 clinical lesions) there is a role for MRI to fulfill the diagnostic criteria by demonstrating dissemination in space, in time or both.

The McDonald criteria are very specific, because if you want to use MRI for the diagnosis of MS, you have to make sure that the patient really has MS.
You do not want a patient to start treatment daily if there is any doubt about the diagnosis.

For dissemination in space (DIS) lesions in two out of four typical areas of the CNS are required:

  1. periventricular
  2. juxtacortical
  3. infratentorial
  4. spinal cord

For dissemination in time (DIT) there are two possibilities:

  1. A new T2 and/or gadolinium-enhancing lesion(s) on follow-up MRI, with reference to a baseline scan, irrespective of the timing of the baseline MRI OR
  2. Simultaneous presence of asymptomatic gadolinium-enhancing and non-enhancing lesions at any time

MRI protocol

MS Brain Protocol

Indications for MRI of the brain are:

  • Clinically isolated syndrome suggestive of MS to prove dissemination in time or space in order to fulfill the McDonald criteria
  • Patients with MS to determine the prognosis or response to therapy
  • To specify an atypical lesion in the spinal cord
  • To screen for opportunistic infections in patients receiving immunosuppressive treatment (for example development of Progressive Multifocal Leukoencephalopthy in patients using natalizumab).

Gadolinium is administered at the start of the examination because the longer you wait the more enhancement you will see on the T1W images (MS lesions are not spontaneously bright on T1-weighted images without contrast administration).
A scout with additional mid-sagittal T1WI is made for optimal and constant positioning.
The sagittal FLAIR is ideal for detection of lesions in the corpus callosum and the 3D sequence allows for better detection of smaller and juxtacortical lesions.
The PD/T2W scan is preferably conventional SE or TSE/FSE.

Finally the axial T1W-images are made after about 15 minutes to provide optimal contrast enhancement.

Coronal and midsagittal scout views are needed for reproducible positioning of the slices, so you are able to compare follow-up studies.
Use the coronal scout to plan the true midsagittal image parallel to the falx and other midline structures.
On a true midsagittal image a line is drawn through the pituitary gland and the roof of the fourth ventricle (fastigium).
This is called the HYFA: hypophysis-fastigium line.
Subsequently the slices are positioned with the middle slice at the lower border of the splenium of the corpus callosum.

MS Spinal cord Protocol

Indications for MRI of the spinal cord are:

  • Cord symptoms
  • To gain specificity in case of non-specific brain lesions

Gadolinium is not necessary when only the spinal cord is examined.
Contrary to the brain there will only rarely be enhancement in the cord.
Only when other diagnoses are considered (e.g. sarcoid) Gd is necessary.
The most diagnostic sequence is the conventional SE or FSE (TSE) PDW, because this is the most sensitive technique.
FLAIR should NOT be used in the spinal cord and will only demonstrate 10% of the lesions.

Prevalence and a priori chance

When we look at the prevalence of the white matter diseases, you will notice that there are enormous differences.

Hereditary diseases are extremely uncommon as individual diseases, but as a group they are not that uncommon, but still far more uncommon than MS.

If we look at the prevalence of Lyme disease, which is a rather popular disease at the moment, then we will notice that it still is a very uncommon disease despite of all the serological tests that are being performed nowadays.

When incidental WMLs are found, these are usually the result of small vessel disease, since up to 50% of patients that get an MR examination for whatever reason, will have WMLs of vascular origin.
They are more common in older people and in patients with vascular risk factors like atherosclerosis, high blood pressure, high cholesterol, diabetes, amyloid angiopathy, hyperhomocysteinemia, atrial fibrillation etc.


If a patient is clinically suspected of having MS and the MR-images support that diagnosis, than you should not consider the possibility of Lyme's disease and neuro-SLE in the differential diagnosis, because they have such a low prevalence.
There must be other ways to impress your colleagues.
These diagnoses are only worth mentioning if there are clinical findings that support these diagnoses.

Consequently, it is not wise to put MS in the differential diagnosis if the clinician does not suspect the patient of having MS and on the MR incidental WMLs are found.
The odds are against the diagnosis of MS, because vascular WMLs are 50-500 times more likely than MS plaques.
On the other hand if a patient is clinically suspected of having MS and multiple WMLs are found, our major concern is the differential diagnosis MS versus vascular disease and we have to follow the McDonald criteria.

Differential diagnosis of WMLs

The differential diagnosis of white matter lesions is extremely long.
In normal ageing WMLs are seen, but most WMLs are acquired and of hypoxic-ischemic origin.
The most common inflammatory disease is Multiple Sclerosis.
The most common viral infections are PML and HIV.
Inherited diseases usually will have symmetrical abnormalities, so they have to be differentiated from intoxications.

DD multiple patchy lesions

On the left a collection of images with multiple punctate and patchy lesions in the WM.
Some will be discussed in more detail.
There is no complete overlap between the images on the left and the text on the right.

Borderzone infarction
Key finding: typically these lesions are located in only one hemisphere, either in deep watershed area or peripheral watershed area. In the case on the left the infarction is in the deep watershed area.

Key findings: Multifocal lesions in WM and basal ganglia 10-14 days following infection or vaccination.
As in MS, ADEM can involve the spinal cord, U-fibers and corpus callosum and sometimes show enhancement.
Different from MS is that the lesions are often large and in a younger age group. The disease is monophasic.

2-3mm lesions simulating MS in a patient with skin rash and influenza-like illness. Other findings are high signal in spinal cord and enhancement of CN7 (root entry zone).

Sarcoid is the great mimicker. The distribution of lesions is quite similar to MS.

Progressive Multifocal Leukoencephalopathy (PML) is a demyelinating disease caused by JC virus in immunosuppressed patients.
Key finding: space-occupying, nonenhancing WMLs in the U-fibers (unlike HIV or CMV).
PML may be unilateral, but more often it is bilateral and asymmetrical.
Click here for more information.

Virchow Robin spaces
Key finding: Bright on T2WI and dark on FLAIR.

Small vessel disease
WMLs in the deep white matter. Not located in corpus callosum, juxtaventricular or juxtacortical.
In many cases there are also

DD multiple enhancing lesions

On the left a collection of images with multiple enhancing lesions in the WM.
Some will be discussed in more detail.
There is no complete overlap between the images on the left and the text on the right.

Most diseases with vasculitis are characterized by punctiform enhancement.
Vasculitis in the brain is seen in SLE, PAN, Behcet, syphilis, Wegener, Sjogren and Primary angiitis of CNS

Behcet is more commonly seen in Turkish patients.
Typical findings are brainstem lesions with nodular enhancement in the acute phase

Metastases are mostly surrounded by a lot of edema.

Borderzone infarction
Peripheral border zone infarctions may enhance in the early phase.


Virchow Robin spaces

First look at the images on the left and describe the lesions.
Then continue.

On the T2W image there are multiple high intensity lesions in the basal ganglia.
On the FLAIR image these lesions are dark, so they follow the intensity of CSF on all sequences (they were hypointense ion the T1WI).
This signal intensity in combination with the location is typical for VR spaces.

FLAIR image

Virchow Robin spaces are CSF spaces around penetrating leptomeningeal vessels.
They are typically located in basal ganglia, around atria, near the anterior commissure and in the middle of the brainstem.
On MR they follow the signal intensity of CSF on all sequences.
They are dark on FLAIR and PD unlike other WMLs.
Usually they are small except around the anterior commissure, where perivascular spaces can be larger.

On this image we see both very wide VR spaces as well as confluent hyperintense lesions in the WM.
This case nicely illustrates the difference between VR spaces and WMLs.
This is an extreme case and this condition is known as etat crible.
VR spaces enlarge with age and hypertension as a result of atrophy of surrounding structures.

Normal aging: Widening of sulci, periventricular caps (arrow) and bands and some punctate WMLs in the deep white matter.

Normal Aging

In normal ageing we can see:

  • Periventricular caps and bands
  • Mild atrophy with widening of sulci and ventricles
  • Punctate and sometimes even confluent lesions in the deep white matter (Fazekas I and II).

Periventricular caps are hyperintense regions around the anterior and posterior pole of the lateral ventricles and are associated with myelin pallor and dilated perivascular spaces.
Periventricular bands or 'rims' are thin linear lesions along the body of the lateral ventricles and are associated with subependymal gliosis.

White matter changes in Fazekas I, II and III.

Normal Aging (2)
The clinical significance of white matter changes in aging has not been fully elucidated.
There is a relationship between several cerebrovascular risk factors and the presence of white matter changes.
One of the strongest risk factors however, apart from hypertension, is that of age.

What is still considered normal depends on the age of the patient.

These white matter changes are classified according to Fazekas:

  1. Mild - punctate WMLs: Fazekas I)
  2. Moderate - confluent WMLs: Fazekas II - in the deep white matter can be considered normal in aging.
  3. Severe - extensive confluent WMLs: Fazekas III - always abnormal.
SE T2WI: multiple WMLs in a hypertensive patient.

Vascular disease

First look at the images on the left and describe the lesions.
Then continue.

The location of these white matter lesions is in the deep white matter and it is important to notice that these lesions are not juxtaventricular, not juxtacortical and not located in the corpus callosum.
Unlike in MS, they do not touch the ventricles or the cortex.
Given the a priori greater chance of hypoxic-ischemic WM lesions, we must conclude that these WMLs probably have a vascular origin.
Only if the clinical findings strongly direct us towards inflammatory, infectious, toxic or other diseases, should we consider these diagnoses.
Suggesting the diagnosis of MS in a patient with these MR findings and with no clinical suspicion for MS would be unwise.

The spinal cord in this patient was normal.
In a patient with vasculitis or ischemia the spinal cord is usually normal, while in a MS patient in more than 90% of the cases it will be abnormal (2).
If the differentiation between a vascular origin of WMLs and MS is difficult for instance in an older patient who is suspected of MS, than an MR of the spinal cord can be helpful (2).

Vascular disease (2)
When we go back to the first case that was shown, it is now very obvious that this is vascular disease.
There is widespread disease in the deep white matter, but the U-fibers and corpus callosum are not involved.

Ischemic WMLs present as lacunar infarcts, watershed infarcts or diffuse hyperintense lesions within the deep white matter.
Lacunar infarcts are due to arteriolar sclerosis of small penetrating medullary arteries.
Watershed infarctions are the result of atherosclerosis of larger vessels, for instance carotid obstruction or the result of hypoperfusion.
Atherosclerotic brain changes are seen in 50% of patients older than 50 years.
They are found in normotensive patients, but more common in hypertensives.


First look at the images and describe the lesions.
Then continue.

The distribution of lesions is quite similar to MS.
Besides lesions in the deep WM, there are some juxtaiventricular lesions and even Dawson finger-like lesions.
The final diagnosis was sarcoid.
Sarcoid has surpassed neurosyphilis as the great mimicker.

Sarcoid (2)
On the left we see the coronal Gd-enhanced T1W images of this patient.
First study these images, than continue.

There is punctate enhancement in the basal nuclei.
This is seen in sarcoid and can also be seen in SLE or other vasculitis.
Typical for sarcoid in this case is the leptomeningeal enhancement (yellow arrow).
This is the result of granulomatous inflammation of the leptomeninges.

Sarcoid (3)
Another typical finding in this same case is the linear enhancement (yellow arrow).
This is due to inflammation along the Virchow Robin spaces.
This is also a form of leptomeningeal enhancement.
This explains why sarcoid has a similar distribution to MS: the Virchow Robin spaces follow the small penetrating veins, which are involved in MS.

Typical skin rash caused by spirochete transmitted by a tick.

Lyme disease

Lyme disease is caused by a spirochete (borreliaBurgdorferi) that is transmitted by a tick.
It first causes a skin rash.
A few months later the spirochete can infect the CNS and MS-like WMLs are seen.

Clinically Lyme presents with acute CNS symptoms (e.g.cranial nerve palsy) and sometimes transverse myelitis.

MS like lesions in Lyme's disease.

Lyme disease (2)
Key finding: 2-3mm lesions simulating MS in a patient with skin rash and influenza-like illness.
Other findings are high signal in spinal cord and enhancement of CN7 (root entry zone).

Natalizumab-associated PML. Images were kindly provided by Bénédicte Quivron CH Jolimont, La Louvière, Belgium.

Natalizumab-associated PML

Progressive Multifocal Leukoencephalopathy (PML) is a demyelinating disease caused by JC virus in immunosuppressed patients.

Natalizumab is a monoclonal antibody against α4-integrin approved for the treatment of multiple sclerosis due to a positive effect on clinical and magnetic resonance imaging (MRI) outcome measures.

A relatively rare but serious side effect of this drug is a higher risk of developing PML.

The diagnosis of PML according to diagnostic criteria is based on the clinical presentation, the identification of JCV DNA in the CNS (e.g., in the cerebrospinal fluid) and imaging findings preferably on MRI.

Compared to other PML populations such as HIV, the imaging findings in natalizumab-associated PML have been described as heterogeneous and fluctuating.

Key imaging signs are:

  • Focal or multifocal lesions in the supratentorial subcortical white matter involving the U-fibers and the cortical grey matter, less frequently posterior fossa and deep grey matter
    • T2-hyperintense (occasionally with small focal lesions in the vicinity of the main lesion)
    • T1-isointese or hypointense depending on the degree of demyelination
    • In approximately 30% of the patients PML lesions can show contrast enhancement.
    • High signal intensity on DWI particularly in the border of the lesions reflecting active infection and swelling of the white matter cells.

It can be difficult to differentiate progressive MS from natalizumab-associated PML.
See table for differences in imaging.

How to image natalizumab-associated PML:

  • FLAIR has the highest sensitivity in the detection of PML lesions
  • T2-weighted sequences can show certain aspects of PML lesions (eg, microcysts)
  • T1 with and without contrast is helpful to assess the degree of demyelination and signs of inflammation.
  • DWI is useful for the detection of active infection.

For further information please see:


Key finding: Atrophy and symmetric periventricular or more diffuse WMLs in AIDS patient


Cadasil is short for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukencephalopathy.
It is an inherited small vessel disease.
Clinical clues: migraine, dementia and family history.

Key finding: subcortical lacunar infarcts with small cystic lesions and leukoencephalopathy in young adults.
Localizations of the WMLs in the anterior temporal pole and external capsule have a high specificity.