Evidence of White Matter Neuroinflammation in [ME/CFS]: A Diffusion-Based Neuroinflammation Imaging Study 2026 Yu et al

[forestglip]

To be reasonably likely to get the results from this study where only one association was significant in univariate but nearly all had significance in multivariate, you’d need 0,1 to generally dominate

If all the different niiXX outcomes are correlated to each other (which we might expect if these are possibly just different effects of a common pathology), then they will tend to have similar results. If the me/cfs_status association with NII-RF has that 0,1 significance pattern, then we can expect others with similar relationships to also have that pattern.

For example, we can imagine testing mecfs association with leukocyte count in four regions of the brain, but the regions are only 1 mm away from each other. Whatever p-value one region has, the others probably will [edit: have very similar p-values] due to them being markers of the same underlying process.

 

[jnmaciuch]

If all the different niiXX outcomes are correlated to each other (which we might expect if these are possibly just different effects of a common pathology), then they will tend to have similar results. If the me/cfs_status association with NII-RF has that 0,1 significance pattern, then we can expect others with similar relationships to also have that pattern.

For example, we can imagine testing mecfs association with leukocyte count in four regions of the brain, but the regions are only 1 mm away from each other. Whatever p-value one region has, the others probably will [edit: have very similar p-values] due to them being markers of the same underlying process.

I think that tends to apply for directionality much more than p-values crossing the threshold. If they are all weak associations from the same process, which they’d have to be to not end up with a predominance of 1,1, then it seems more likely to get a more even mix of 0,1 and 0,0 if some are on the slightly weaker side. You may be able to finesse all 0,1 in a simulation but I think I’ve seen enough transcriptomic data sets where an entire pathway is upregulated but only 2/30 genes pass significance

 

[forestglip]

I think that tends to apply for directionality much more than p-values crossing the threshold. If they are all weak associations from the same process, which they’d have to be to not end up with a predominance of 1,1, then it seems more likely to get a mix of 0,1 and 0,0

It should apply to both. They may be weak associations with ME/CFS status, but still very strong associations with each other. For example, if the data for NII-RF was accidentally copied and replaced the data for NII-HR, making them identical, then NII-RF would still have a relatively weak association with ME/CFS, but due to the perfect correlation between NII-RF and NII-HR, the p-value would be identical for NII-HR.

I don't know how correlated these brain metrics are to each other, but the larger the correlation, the more similar the p-values and coefficients will tend to be between these models.

 

[ME/CFS Science Blog]

And there is no plausible reason to control for anxiety and depression,

Suspect they did this to rule out that comorbid anxiety or depression were driving the effect.

Bit of a longshot but perhaps the increase of significant results after controlling for potential confounders was due to anxiety/depression having an opposite effect to ME/CFS? Or (also speculative) perhaps the effect was mostly present in mild ME/CFS patients, so controlling for anxiety/depression (which correlate with ME/CFS severity) makes the relationship clearer?

 

[ME/CFS Science Blog]

Still confused about what the hindered fraction means and how it relates to edema. Some papers describe it as follows:

Free water, such as within a ventricle, is represented by the isotropic diffusion tensor components with ADC of free diffusion. Isotropic diffusion tensors with intermediate diffusivity between the restricted diffusivity of cells and the free diffusivity of ventricular fluid capture diffusion profiles of the intra-voxel compartments of vasogenic edema and tissue loss (Chiang et al., 2014). We have referred to this as “hindered” diffusion

Source: "A new imaging modality to non-invasively assess multiple sclerosis pathology" - PubMed

The current ME/CFS paper defines it as:

NII-derived hindered water ratio, is the hindered fraction of non-restricted isotropic diffusion (0.3.<D≤2.5μm2/ms)

But other papers described a similar interval as the non-restricted isotropic diffusion and an indicator of vasogenic edema.

Based on our previous experimental findings, the restricted isotropic diffusion fraction reflecting cellularity is derived by the summation of f(D) at 0 ≤ ADC ≤ 0.3 μm2/ms. The summation of the remaining f(D) at 3 > ADC > 0.3 μm2/ms was assigned to non-restricted isotropic diffusion reflecting vasogenic edema and CSF water

Source: Quantifying white matter tract diffusion parameters in the presence of increased extra-fiber cellularity and vasogenic edema - PubMed

So does the decreased hindered fraction in ME/CFS patients indicate edema as seen in inflammation or the opposite?

 

[ME/CFS Science Blog]

To add to the confusion the obesity paper defined the 'DBSI-hindered fraction' as > 0.3 µm2/ms;

By solving the DBSI model, we obtain a group of anisotropic and isotropic metrics that include: DBSI-FA (indicates overall WM integrity), DBSIAD (indicates axonal loss/injury), DBSI-RD (indicates myelin loss), DBSI-fiber fraction or DBSI-FF (indicates apparent axonal density), DBSI-RF (D ≤ 0.3 µm2/ms; indicates inflammationrelated cellularity), and DBSI-hindered fraction or DBSI-HF(D > 0.3 µm2/ms; indicates extracellular tissue edema).

Source: Neuroinflammation and White Matter Alterations in Obesity Assessed by Diffusion Basis Spectrum Imaging - PubMed

So as @ScoutB already highlighted, why does the current ME/CFS paper put the limit at 2.5μm2/ms and why doesn't it mention or speak about anything that has more diffusion than this?

 

[jnmaciuch]

For example, if the data for NII-RF was accidentally copied and replaced the data for NII-HR, making them identical, then NII-RF would still have a relatively weak association with ME/CFS, but due to the perfect correlation between NII-RF and NII-HR, the p-value would be identical for NII-HR.

yeah that would be the type of human error I was suggesting

I don't know how correlated these brain metrics are to each other, but the larger the correlation, the more similar the p-values and coefficients will tend to be between these models.

I think we can rule out a naturally-occurring scenario like this for this thread’s study since when the measurements were significant, there tended to be repetition in the regions, but not all the same regions came up for each measurement. Meaning that the measurements are probably intercorrelated, and what you end up seeing p-value-wise is a mix of some measurements reaching significance and some not reaching that threshold.

 

[ME/CFS Science Blog]

My guess is that signs of edema would show up as an increase in the isotropic hindered fraction (0.3.<D≤2.5μm2/ms). But in ME/CFS this was decreased instead of increased.

As Hutan explained, the same goes for the isometric restricted fraction (D≤0.3μm2/ms). This is water that could go any direction but is very restricted because it is contained in cells. It's an indicator of immune cell infiltration. But in ME/CFS this was decreased instead of increased.

So both isometric fractions mentioned in this paper were decreased. What was increased was the anisotropic diffusion which the paper describes as "fibre fraction (NII-FF, indicating apparent axonal density)." This are water molecules inside or close to axons because they clearly move in a direction. In inflammation NII-FF is often reduced e.g. due to damage to axons or because more isotropic water molecules coming in. In ME/CFS, however, it was increased.

So I think it all shows the opposite of inflammation, more like increased connectivity or axons being more tightly packed.

The overall equation is something like:

Diffusion = fraction anisotropic + fraction isometric restricted + fraction isometric unrestricted = 1

In inflammation the isometric parts are increased because of cell infiltration and edema while the anistropic part is decreased. In ME/CFS it's just the opposite. There is less isometric water and more water moving in a particular direction.

 

[Jonathan Edwards]

My guess is that signs of edema would show up as an increase in the isotropic hindered fraction (0.3.<D≤2.5μm2/ms). But in ME/CFS this was decreased instead of increased.

I wonder if part of the problem is that extracellular water, increased in inflammation, tends to be mostly 'hindered' in that the water molecules will be intermittently binding to matrix, slowing diffusion, and also geometrically limited by gel elements in the matrix and cells when they are moving about. Truly free or unhindered water may be a small fraction. In fact it may be in a sense a mathematical artefact to propose a separate free component in the water molecules are bound to constantly shift between compartments.

The upshot may be that in inflammation 'hindered water' goes up as a total because extracellular water is now a bigger fraction of the total (the rest being cellular restricted water and anisotropic intracellular water (which must also be partly hindered but maybe that is ignored). This seems paradoxical because we tend to think of inflammation introducing 'free' water. The free fraction may go up even more than the hindered fraction but if still small it may not be a useful measure?

For the hindered fraction to go down you would either need more restricted water or anisotropic water or you could have more truly free water. Maybe the situation in ME/CFS is more truly free water - which might be in glymphatics or just interstitium that has got waterier to the extent that the notional free fraction is noticeable.

I have no idea which it is - and I do think the authors could have done better to make their techniques more intelligible. The key question is whether or not they themselves understand their significance.

 

[ME/CFS Science Blog]

For the hindered fraction to go down you would either need more restricted water or anisotropic water or you could have more truly free water. Maybe the situation in ME/CFS is more truly free water - which might be in glymphatics or just interstitium that has got waterier to the extent that the notional free fraction is noticeable.

I'm not that good at math but I think the very free water (with diffusion > 2.5 μm2/ms) doesn't even enter their equation.

The second part represents the isotropic components, an integral from a to b where "a and b are the low and high diffusivity limits for the isotropic diffusion spectrum f(D)." Given the further explanation in the text, one is tempted to assume that a = 0.3 and b = 2.5 μm2/ms. That would explain why the free fraction is never mention in the paper.

So if this isn't included in the equation, then in ME/CFS it must that there's relatively more anisotropic than isotropic water.

 

[Jonathan Edwards]

So if this isn't included in the equation, then in ME/CFS it must that there's relatively more anisotropic than isotropic water.

OK. And I would worry that simple assumptions about which is inside and which is outside cells could be badly wrong for white matter. I think we need someone who works with these things to explain what is really going on. SNTG may be able to but It sounds as if even he is a bit bothered by what it means.

 

[jnmaciuch]

Havent been able to read back over the whole thread—has it been explained how restricted fraction differentiates between water trapped in immune cells vs water trapped in neuron soma, astrocyte bodies, etc?

 

[Jonathan Edwards]

Havent been able to read back over the whole thread—has it been explained how restricted fraction differentiates between water trapped in immune cells vs water trapped in neuron soma, astrocyte bodies, etc?

I don't think so. The amount of water in neuron cell bodies is unlikely to change much I think. More restricted isotropic water, if intracellular, might logically indicate new cells coming in. Astrocytes might change in water content significantly because they deal with housekeeping and might need to increase cytoplasmic volume considerably. But even the assumption that restricted water has to be in cells seems fragile to me.

Neuronal fibres/axons would be expected to be anisotropic and not spherically restricted, but axons are full of microtubules and I suspect the water would be seriously 'hindered'. (That may be taken care of.)

I think we need to know how much all these factors have been satisfactorily correlated with a whole range of different physiologic changes, including several types of inflammation.

 

[Jaybee00]

Is someone able to summarize the discussion here in simpler English at some point for those of us with lower IQ’s? Are the study’s findings debunkable?

 

[jnmaciuch]

More restricted isotropic water, if intracellular, might logically indicate new cells coming in.

I think its a reasonable assumption if you have reasonable likelihood of infiltration actually happening. What I'm puzzled by (and it seems I'm not alone in this) is how to interpret lower RF compared to controls when controls probably have no infiltration.

Astrocytes might change in water content significantly because they deal with housekeeping and might need to increase cytoplasmic volume considerably.

Yes that's my main thought--from the earlier glymphatics discussion, it seems like astrocytes serve as a buffer zone for water to help the parenchymal space maintain a fairly constant concentration. They do not change size fast enough to be particularly important to fluid flow but they have been observed to swell and contract dramatically. So my thought is that any restriction fraction seen in healthy brains is likely to represent what is stored in astrocytes.

But even the assumption that restricted water has to be in cells seems fragile to me.

I guess the question is what else? My instinct says it would have to be a small space enclosed in hydrophobic boundaries.

 

[ME/CFS Science Blog]

Is someone able to summarize the discussion here in simpler English at some point for those of us with lower IQ’s? Is the study debunkable?

There are two lines of dicussions.

One is about the statistics. We find it weird that there were more significant findings when confounders like age, sex, depression, anxiety were added to the model. It's possible that this happens but usually adding confounders like this will result in less significant results, not more. There were also some concerns that they excluded 9 ME/CFS patients that could not be matched to healthy controls and how these were selected.

The other discussion is about the interpretation of the data. The authors argue that their findings suggest neuro-inflammation but if we look those up they suggest the opposite.

• ME/CFS patients for example had relatively fewer water molecules that can move in any direction (isotropic) and are confined to tight spaces (restricted). Previous studies assumed that this might reflect water molecules trapped inside cells. So this measure could be seen as an indicator of immune cell infiltration, there being more cells. But in inflammation this measure is increased while in ME/CFS it was decreased.
  
  
• The same with water molecules that can move in any direction (isotropic) but aren't restricted. This has been used as an indicator of edema, water flowing into tissue. Some studies reported this to be increased in inflammation but in ME/CFS it was decreased.
  
  
• What was increased in ME/CFS was water molecules flowing in a particular direction (anisotropic). These are assumed to be water molecules in axons: they are trapped in a tube and can only go in one direction. In inflammation this is sometimes decreased but in ME/CFS it was increased.

So the results do not fully match the explanations that the resarchers give to them, and sometimes it looks to be the complete opposite. Hutan has been in touch with with them so hopefully they can provide an explanation. It could also be that our interpretation is erroneous because the methods are quite new and complex.

 

[Jaybee00]

Thanks!

 

[Jonathan Edwards]

What I'm puzzled by (and it seems I'm not alone in this) is how to interpret lower RF compared to controls when controls probably have no infiltration.

That would fit with more extracellular water )assuming everything is proportions) but agree it doesn't fit with more cells.

 

[Jonathan Edwards]

I guess the question is what else? My instinct says it would have to be a small space enclosed in hydrophobic boundaries.

There is lots of water in extracellular matrix that doesn't move much - bound to sulphate residues etc.. But if it exchanges with other compartments very quickly then the separate phase may not be apparent. I spent about ten years working on water compartments before MRI became available. The most important thing I learnt was how complicated and counterintuitive it all was, even if the biological solutions had a simple elegance. The next thing I learnt was that almost everyone working in the field of water phases in articular tissue had all their basic concepts wrong. But five years later they admitted their mistakes. My recent foray into brain water with various eminent Norwegian groups suggests that none of them understand diffusion!!

 

[jnmaciuch]

That would fit with more extracellular water )assuming everything is proportions) but agree it doesn't fit with more cells.

Ah okay I see the previous discussion about hindered fraction now. So the mystery is how you get a bigger proportion of extracellular water without an increased in hindered fraction

There is lots of water in extracellular matrix that doesn't move much - bound to sulphate residues etc.. But if it exchanges with other compartments very quickly then the separate phase may not be apparent. I spent about ten years working on water compartments before MRI became available. The most important thing I learnt was how complicated and counterintuitive it all was, even if the biological solutions had a simple elegance. The next thing I learnt was that almost everyone working in the field of water phases in articular tissue had all their basic concepts wrong. But five years later they admitted their mistakes. My recent foray into brain water with various eminent Norwegian groups suggests that none of them understand diffusion!!

so it would have to be water in an extracellular matrix that doesn't exchange much with other compartments to end up in the restricted fraction