Can Delivery Cause Relapses in Multiple Sclerosis?

Jane Smith (a pseudonym to protect her identity), was diagnosed with Multiple Sclerosis (MS) as a young woman, but by the time she was pregnant with her first child, it was well-controlled through medication. The medication she was on, Aubagio, was not safe for a developing fetus nor a breastfeeding child, so she was forced to discontinue her medication for the duration of the pregnancy and post-partum breastfeeding period. Despite this, her pregnancy was uneventful with no relapses of her MS, but shortly after she started breastfeeding her newborn baby her symptoms resumed in earnest. Had breastfeeding somehow made her MS worse? Jane had to resume her medication after breastfeeding for only one month, despite preferring to continue breastfeeding.

To answer whether breastfeeding made Jane experience an MS relapse, we first need to get a better understanding of MS. MS is an autoimmune disease that is not fully understood and is hotly debated in the scientific world, but it certainly involves immune cells making their way into the brain and attacking the fatty insulating sheaths that make our brain cells—neurons—conduct signals quickly between regions of the brain.¹ Why these immune cells are crossing the blood-brain barrier, which normally prevents this from occurring, and why they are primed towards targeting the myelin sheaths is not well understood. Once one of these immune cell attacks occur, the damage to that region of the brain can be long-lasting and extensive, leading to scarring and long-term partial loss of function for that area, or it can largely resolve to pre-relapse levels.¹

Generally, instances of immune cells crossing; causing damage, inflammation, and scarring; and then quieting down coincide with clinical events where patients experience a surge of symptoms that we call relapses. These relapses represent debilitating but temporary loss of function while the brain is inflamed, that then largely resolves after a period, ranging between 24-hours to around 4 weeks.¹ Relapses are the hallmark of Relapsing-Remitting MS, which is standard form of MS, and have been involved in the clinical diagnostic criteria since its first description by Charcot in 1868.² Relapses are also the clinical target of most MS medications. In fact, the most potent medications on the market today are associated with almost no relapses in patients.^3,4

Jane, having been off her medication for the duration of her pregnancy, was certainly no longer under its protective effect, but the timing of the symptom worsening is still suspicious. Why did her symptoms get so much worse only after she started breastfeeding?

The first possibility to rule out is an Aubagio-rebound syndrome. This is a phenomenon that is not well documented, but a few doctors have reported cases of individual patients experiencing significant worsening of their MS shortly after discontinuing Aubagio.^5-7 However, even the doctors reporting these instances question whether they are truly a worsening following the cessation of the drug or whether there are other factors influencing this. Additionally, in most rebound syndromes, we would expect to see the effect within 24 weeks, significantly shorter than the ninth months that Jane was off medication for.

A potentially novel alternative focuses more on the role hormones play in MS. During pregnancy, women produce continually increasing levels of estrogen which suddenly drop following delivery.⁸ During this time, it is entirely feasible that the pregnant mother slowly experiences a degree of estrogen desensitization, where her body stops responding as directly to the presence of estrogen. Desensitization is a general term for the process where something, be it a body or a receptor, becomes less sensitive to a stimulus over time.^9,10 You experience desensitization if you walk into a room that smells unpleasant, but 15 minutes later you don’t even notice the smell. This process applies over a range of timescales and systems, but in the case of a hormone receptors, several weeks at elevated levels would be enough to downregulate the receptors.¹¹ Unfortunately, that timeline lines up closely with pregnancy, and after estrogen levels return to normal following delivery, the fact that Jane could have been desensitized to estrogen means that the normal levels of estrogen were likely not causing the normal level of response from her body. In other words, while Jane may have had normal levels of estrogen in her bloodstream, her body would have been acting like the levels of estrogen were much lower than normal.