(Note: this essay is concerned with the general widespread personality change which may occur independently of the anatomical site of the lesions. The lesions themselves may cause character change very specific to the person with the disease. This essay does not treat with this.)

Stereotypic changes in personality in people with aggressive MS have long been recognized. Sometimes these personality changes continue within remissions; this happened with Sarah: I recognised that she was not herself even while she was able to walk for miles. To look back at those times is not easy. I was aware that I was looking at the very same mental state which I had seen in others with MS. Here is an excellent paper which examines this phenomenon, which is not accounted for by demyelination. [Benedict, RHB et al., Personality Disorder in Multiple Sclerosis correlates with cognitive impairment. J Neuropsychiatry Clin Neurosci 2001; 13: 70 - 76. Full pdf available link ] These authors come to the conclusion that this personality change (which is, they say, characterised by elevated neuroticism and reduction in empathy, agreeableness and conscientiousness) is due to 'a neurogenic frontal lobe syndrome.' I think that the word which best sums up the character-changes is insouciance: a nonchalant lack of concern.

Not everyone with MS comes to have this syndrome; it seems only to occur prior to and during an actively progressive phase. It cannot be accounted for by primary autoimmune myelinopathy. I believe it likely to be a toxic state due to bacterial metabolites; there is some indirect evidence for this. Let's look at this more deeply.

Our cells live in a fairly rigorously controlled milieu, a world where homeostasis is important. Our cells are therefore very careful as to what they allow out into the extracellular fluid. Sometimes in disease this concern breaks down: in liver failure, volatiles are released into the general circulation (they can be smelled on the breath - the so-called fetor hepaticus.) When they reach the brain they cause symptoms of hepatic encephalopathy. This has an insidious onset, with cognitive impairment and a reversal of day/night sleep rhythms. Spatial awareness is compromised.

Unlike our cells, bacteria do not generally live in a homeostatic environment: they may even find an evolutionary advantage in pumping toxic compounds into their environment. The student of bacteriology quickly recognises the unique smell which many bacterial species or genera possess. These smells are due to volatile organic compounds.

Volatile toxins tend to affect the higher centres which form the personality first; think of alcohol and anaesthetic agents. Interestingly, a minority of people with MS personality change become disinhibited and take risks. As with intoxication with volatiles, personality changes in MS are marked by a profound elongation of reaction times.

Finally, there is the effect of antibiotics. Sarah had very aggressive disease, and had lost insight into it. On starting doxycycline she became delirious for some five days. Then she began to lose that MS personality change. I began to see something of her old self. It was like seeing someone leaving a prison cell.

I have to say that, in my experience, those who comply with treatment rapidly lose this strange mental state. Indeed, those who retain it are generally found, on close questioning, to have abandoned treatment. And that's the rub. Some people don't like losing the feeling of euphoria where their disabilities don't really matter and where the future is unimportant. The cold light of reality can be too much to bear. It is possible to conjecture that a state of addiction may occur, from which withdrawal may be painful. That is why a diligent and attentive carer is so important. The antibiotics must be seen to be swallowed.

NEW

Indeed, recent research shows that specific volatiles (tentatively hexanal and 5-methyl undecane) are found in the breath of persons with MS [Ionescu R et al. Detection of multiple sclerosis from exhaled breath using bilayers of polycyclic aromatic hydrocarbons and single-wall carbon nanotubes. ACS Chem Neurosci. 2011 Dec 21;2(12):687-93. Epub 2011 Sep 22.] Hexanal (hexanaldehyde) is a molecule associated with lipid peroxidation and is found in rancid foodstuffs.