Experts view MS brain fog as multifactorial, meaning there is rarely a single cause. Instead, cognitive symptoms often stem from a combination of MS-related brain changes and other medical, emotional, and lifestyle factors.
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MS-Related Changes in the Brain
MS affects both white and gray matter, disrupting how efficiently the brain processes information. Lesions, loss of brain volume, and changes in structures such as the thalamus, frontal lobes, and hippocampus can all affect thinking and memory.
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Recent research shows that MS cognitive symptoms may reflect disruptions in brain networks, not just isolated areas. When the networks responsible for attention, planning, and memory become less efficient, the brain must work harder, creating a sense of mental effort or slow thinking.
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Fatigue and Cognitive Energy
Fatigue is one of the most disabling MS symptoms and can strongly affect cognition. Cognitive fatigue occurs when the brain becomes less able to sustain attention or mental effort over time. Research suggests that disruptions in neurotransmitter systems, including noradrenaline pathways involved in alertness and motivation, may contribute.
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Fatigue is a common symptom that can make many aspects of MS more difficult, including brain fog, says Stropp.
Mood and Stress
Depression, anxiety, and chronic stress are more common in people with MS than in the general population. Research suggests that as many as half of all people with MS will have depression or anxiety at some point.
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“Mood disorders can impact concentration, attention, and memory in people with MS,” Stropp says.
Sleep Problems
Research suggests that sleep problems, including sleep apnea and insomnia, may contribute to cognitive decline in MS. Women with MS and sleep disorders were more likely to have trouble following instructions and conversations, and to have memory issues.
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“If someone with MS brings up a cognitive concern, sleep is something we focus on very early on. Sometimes we will be able to see classic signs of sleep apnea, like loud snoring, but sometimes we have to dig more. Sleep apnea can be quiet and not have those typical symptoms,” says Stropp.
Medications
Some medications used to treat MS symptoms can contribute to fogginess, including drugs for neuropathic pain, migraine, spasticity, and bladder symptoms.
“It’s a good idea to go through your medication list with your neurologist to see if any of your cognitive issues could be a side effect of a drug you’re taking,” says Stropp.
Migraine
MS doesn’t cause migraine, but it is more common in people with MS, says Stropp. “If someone has severe migraines that aren’t well controlled, that can create its own version of cognitive cloudiness,” she says.
Menopause
Perimenopause and menopause often overlap with the age when many people reach progressive stages of MS — and brain fog is also a symptom of menopause.
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“It can be almost impossible to distinguish menopause-related symptoms from MS ones based on how they feel,” says Stropp.
