Other causes of memory and thinking problems
About dementia diagnosis
There are many other common conditions that can lead to memory and thinking problems. This page explains some of them.
In this section:
If you’re worried you or a loved one may be experiencing symptoms of the conditions listed on this page, a doctor can test for these conditions to ensure that a correct diagnosis is given.
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Vitamin B12 deficiency
When someone has a vitamin B12 deficiency, their red blood cells don’t function properly. Red blood cells carry oxygen around the body, delivering it to cells to make energy.
When red blood cells are not working normally, their ability to carry oxygen is also affected. When cells don’t receive enough oxygen from the blood, it can cause problems in several parts of the body.
Vitamin B12 deficiency is thought to affect around six in 100 people under 60 years old and around 20 in 100 older people in the UK.
Some people are unable to absorb vitamin B12 due to:
- certain genetic disorders
- medical conditions such as pernicious anaemia
- as a result of taking prescription drugs like metformin
- Intestinal disorders such as Crohn’s disease.
Common sources of B12 include meat, eggs, and dairy. People who do not eat meat and dairy may not get enough B12 through their diet.
Alternative sources include some soy products and fortified breakfast cereals.
Hypothyroidism
Your thyroid gland makes hormones that help control how your body uses energy.
These hormones help manage your metabolism, which is how your body changes the food you eat into energy you can use.
Hypothyroidism, or an underactive thyroid, is a disorder where your thyroid gland stops producing enough hormones.
Hypothyroidism is not a type of dementia, but its symptoms can be similar. There are many causes of hypothyroidism, such as:
- having an autoimmune condition called Hashimoto’s disease.
- having radiotherapy in your neck area.
- Someone may also be more likely to have an underactive thyroid if there is a family history of it.
Hypothyroidism is thought to affect three in every 100 people in the UK. It is 10 times more common in women than men.
Encephalitis
Encephalitis is the medical term for when the brain becomes inflamed.
There are rare occasions where encephalitis can cause dementia-like symptoms.
One cause of encephalitis is autoimmunity. Autoimmunity is where the immune system attacks the body’s tissues instead of defending them.
With autoimmune encephalitis, the immune system mistakenly attacks the surface of the brain, also known as the cortex.
The cortex responds to the attack by becoming inflamed, leading to symptoms of encephalitis.
Other causes of encephalitis can be from:
- viral, bacterial or fungal infections
- diseases spread from the bite of mosquitoes, ticks or other infected animals.
Encephalitis affects around 4,000 people each year in the United Kingdom. That is less than six cases per 100,000 people.
Multiple sclerosis (MS)
Multiple sclerosis (MS) is an autoimmune, neurological disease affecting the brain and spinal cord.
An autoimmune disease is where the immune systems attacks the body’s tissues instead of defending them.
MS is not a type of dementia, but it can cause similar symptoms. This is because it affects the brain and spinal cord.
MS is thought to affect over 100,000 people in the UK. It usually develops before the age of 40. It affects more woman than men.
MS damages to the white matter in the brain. White matter is made up of nerve fibres covered by a protective layer of fat called myelin.
In MS, the immune system attacks the myelin, exposing the nerve fibres which affects the way they work.
Niemann-Pick disease type C
Niemann-Pick disease type C (NPC) is a rare, inherited condition that prevents cholesterol and other fats from moving around the body properly.
This leads to a build-up of fat inside cells in the liver, spleen, and brain.
NPC is caused by inheriting two copies of a faulty NPC gene, one from their mother, and one from their father. Someone with just one of these copies, a ‘carrier’, will not be affected by the disease.
NPC is thought to affect one in 100,000 people in the UK.
It is not a type of dementia, but symptoms can be similar.
Normal pressure hydrocephalus (NPH)
Spinal fluid usually circulates around the brain and spinal cord.
Normal pressure hydrocephalus occurs when spinal fluid builds up inside hollow, fluid-filled spaces in the brain called ventricles. As ventricles enlarge, they can damage the surrounding brain tissue.
In most cases there is no obvious cause, known as idiopathic NPH.
However, the condition can happen after a stroke, head injury or meningitis.
NPH is very rare and mostly affects people over 60, but the right treatment can often reverse the symptoms.
HIV-related cognitive impairment
HIV (human immunodeficiency virus) is an infection that weakens the body’s immune system.
It is estimated that there are around 111,800 people living with HIV in the UK. That is less than two cases of HIV per 1,000 people.
HIV-related cognitive impairment is a condition that falls within the spectrum of HIV-associated neurocognitive disorders (HAND).
HIV is not a type of dementia, but it can cause similar symptoms. Doctors call this HIV-related cognitive impairment.
Antiretroviral drugs for the treatment of HIV have improved significantly in recent years.
This means that the number of people with HIV who go on to develop AIDS (acquired immunodeficiency syndrome) has fallen dramatically.
Because of this, there has also been a fall in the rate of HIV-related cognitive impairment.
This information was updated in February 2026 and is due for review in August 2027. It was written by Alzheimer's Research UK's Information Services team with input from lay and expert reviewers. Please get in touch if you'd like a referenced copy.
This information is produced with support from The Perfume Shop who had no input into the content.
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