Dawson's fingers

Dawson's Fingers appearing on an MRI scan

"Dawson's Fingers" is the name for the multiple sclerosis lesions around the ventricle-based brain veins^[1][2] of Multiple Sclerosis patients. The condition is supposed to be the result of inflammation or mechanical damage by blood pressure^[3]around long axis of medular veins.

Dawson's fingers spread along, and from, large periventricular collecting veins, and are attributed to perivenular inflammation^[4]. Lesions far away from these veins are known as Steiner's splashes^[3].

Distribution

Demyelinization by MS. The Klüver-Barrera colored tissue show a clear decoloration in the area of the lesion (Original scale 1:100)

Using high field MRI system, with several variants several areas show lesions, and can be spacially classified in infratentorial, callosal, juxtacortical, periventricular, and other white matter areas^[5]. Other authors simplify this in three regions: intracortical, mixed gray-white matter, and juxtacortical^[6]. Others classify them as hippocampal, cortical, and WM lesions^[7], and finally, others give seven areas: intracortical, mixed white matter-gray matter, juxtacortical, deep gray matter, periventricular white matter, deep white matter, and infratentorial lesions^[8]. The distribution of the lesions could be linked to the clinical evolution^[9]

Post-mortem authopsy reveal that gray matter demyelination occurs in the motor cortex, cingulate gyrus, cerebellum, thalamus and spinal cord^[10]. Cortical lesions have been observed specially in people with SPMS but they also appear in RRMS and clinically isolated syndrome. They are more frequent in men than in women^[11] and they can partly explain cognitive deficits.

It is known that two parameters of the cortical lesions, fractional anisotropy (FA) and mean diffusivity (MD), are higher in patients than in controls^[12]. They are larger in SPMS than in RRMS and most of them remain unchanged for short follow-up periods. They do not spread into the subcortical white matter and never show gadolinium enhancement. Over a one-year period, CLs can increase their number and size in a relevant proportion of MS patients, without spreading into the subcortical white matter or showing inflammatory features similar to those of white matter lesions.^[13]

The first plausible explanation of their distribution was published by Dr. Schelling. He said:

The specific brain plaques of multiple sclerosis can only be caused by energetic venous back-jets set in motion by intermittent rises in the pressure in the large collecting veins of the neck, but especially of the chest.^[3].

But no problems with chest veins was ever found.

Recently, it has been remarked that it can plausibly be accounted for by veno-venous reflux^[14][15], according to the CCSVI theory. This results in a finger-like appearance of the lesions extending mainly off the ventricles within the brain.

This morphologic appearance was named Dawson's fingers by Charles Lumsden, after the Scottish pathologist James Walker Dawson ^[16], who first defined the condition in 1916.

Demyelination process

Demyelinization by MS. The CD68 colored tissue shows several Macrophages in the area of the lesion. Original scale 1:100

Demyelination begins with the blood-brain barrier breakdown. It is a tight vascular barrier between the blood and brain that should prevent the passage of antibodies through it, but in MS patients it does not work. For unknown reasons special areas appear in the brain and spine, followed by leaks in the blood-brain barrier where immune cells infiltrate.

According to the view of most researchers, a special subset of lymphocytes, called T helper cells, specifically Th1 and Th17^[17], play a key role in the development of the lesion. Under normal circumstances, these lymphocytes can distinguish between self and non-self. However, in a person with MS, these cells recognize healthy parts of the central nervous system as foreign and attack them as if they were an invading virus, triggering inflammatory processes and stimulating other immune cells and soluble factors like cytokines and antibodies. Many of the myelin-recognizing T cells belong to a terminally differentiated subset called co-stimulation-independent effector-memory T cells^{[18][19][20][21][22][23][24][25][26][27][28]}. Recently other type of immune cells, B Cells, have been also implicated in the pathogenesis of MS^[29] and in the degeneration of the axons^[30].

The axons themselves can also be damaged by the attacks.^[31] Often, the brain is able to compensate for some of this damage, due to an ability called neuroplasticity. MS symptoms develop as the cumulative result of multiple lesions in the brain and spinal cord. This is why symptoms can vary greatly between different individuals, depending on where their lesions occur.

Repair processes, called remyelination, also play an important role in MS. Remyelination is one of the reasons why, especially in early phases of the disease, symptoms tend to decrease or disappear temporarily. Nevertheless, nerve damage and irreversible loss of neurons occur early in MS.

The oligodendrocytes that originally formed a myelin sheath cannot completely rebuild a destroyed myelin sheath. However, the central nervous system can recruit oligodendrocyte stem cells capable of proliferation and migration and differentiation into mature myelinating oligodendrocytes. The newly-formed myelin sheaths are thinner and often not as effective as the original ones. Repeated attacks lead to successively fewer effective remyelinations, until a scar-like plaque is built up around the damaged axons. Under laboratory conditions, stem cells are quite capable of proliferating and differentiating into remyelinating oligodendrocytes; it is therefore suspected that inflammatory conditions or axonal damage somehow inhibit stem cell proliferation and differentiation in affected areas^[32]

See also

• Pathophysiology of multiple sclerosis
• Internal cerebral veins
• Great cerebral vein
• Circle of Willis

External links

• Dawson Fingers in Multiple Sclerosis [7]

Sources

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