Multiple myeloma is a type of cancer affecting the plasma cells, which are a type of white blood cell. It can cause mental confusion in some people.

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Multiple myeloma (MM) alters the way a person’s bone marrow produces plasma cells. Instead of creating healthy cells, it makes abnormal cells that crowd out the healthy ones.

Initially, a person with MM may have no symptoms. A doctor may diagnose the disease after a routine blood test.

As the disease progresses, a person may have more symptoms. MM can affect the kidneys, cause the blood to thicken, increase calcium levels in the blood, and more.

This can cause reduced blood flow to the brain, as well as nerve damage. As a result, people with MM may experience mental confusion.

This article discusses the symptoms and side effects of MM that can cause changes in a person’s mental state. Read more to learn about mental confusion in people with multiple myeloma, why it happens, and when to contact a doctor.

In the early stages of the disease, some people have no symptoms. Sometimes, it is incidentally detected by a routine blood test.

People who do have symptoms may experience fatigue and bone pain, which are two common signs of the condition.

Other early symptoms of MM include:

  • frequent bone fractures or breaks
  • fatigue and weakness
  • frequent infections

Yes, mental confusion can be a sign of MM. There are several possible causes for this, including the condition itself, the stress of living with the condition, and the side effects of treatment.

People with MM may feel mental confusion symptoms to different degrees. Mental confusion is frequently called cognitive decline or dysfunction, which includes affecting a person’s executive function and memory.

They may experience mental fogginess, have difficulty remembering things, and not feel like themselves.

Multiple myeloma can cause mental confusion for a variety of reasons. Some of these include features of the disease such as hyperviscosity (thick blood), kidney failure, and high levels of calcium in the blood. Certain treatments for MM can also cause mental confusion in some people.


When people have MM, their bodies produce an excess amount of abnormal proteins. These can build up in the blood, which makes it thicker than normal. This is called hyperviscosity.

When the blood is too thick, it does not flow as freely as usual. The slower blood flow decreases blood flow to the brain, causing mental confusion and dizziness.

According to one 2013 study, about 2–6% of participants with myeloma had symptomatic hyperviscosity. They experienced headaches, dizziness, and changes in vision.

In rare cases, hyperviscosity may cause stroke-like symptoms. These can include slurred speech and weakness on one side of the body.

Kidney failure

In some people with MM, the abnormal myeloma proteins damage the kidneys. When blood with myeloma proteins passes through the kidney’s filters, the proteins enter the tubules (pipes). They can join up with other proteins, causing blockages in the pipes, and eventually kidney failure.

The abnormal proteins can also cause inflammation in the kidneys.

People with kidney disease may experience mental confusion. For example, the electrolyte imbalance associated with kidney problems can cause delirium. Additionally, one older 2008 study reports people with chronic kidney disease (CKD) may also have an increased likelihood of having depression, anxiety, and suicidal thoughts.

Kidney disease is relatively common in people with MM. One study reported about half of people with MM has some degree of kidney problems.

Although initially, an individual may have no symptoms, they can appear over time. A person may experience symptoms including:

  • weakness
  • itching
  • leg swelling
  • shortness of breath

Learn more about the symptoms of kidney failure.


Hypercalcemia is a condition where an individual elevated calcium levels in their blood. This can cause encephalopathy, a disease affecting the brain.

Encephalopathy alters brain function or structure, and it can cause mental confusion.

Hypercalcemia is a serious complication. A 2020 study of people under 65 with multiple myeloma found that the people with hypercalcemia had lower survival rates than those who did not.

One earlier 2011 study found that both chronic and acute hypercalcemia affects the nerve synapses. The synapses are tiny gaps at the end of each nerve cell, and they allow signals to pass between the cells. When the synapses cannot communicate properly, the brain and body cannot function properly.

In addition to mental confusion, hypercalcemia can cause:

  • excessive urination
  • extreme thirst
  • dehydration
  • severe constipation
  • abdominal pain
  • kidney problems or kidney failure
  • weakness
  • loss of appetite
  • confusion
  • feeling drowsy

People with symptoms of hypercalcemia should contact a doctor.

Learn more about the symptoms of hypercalcemia.


MM treatments can affect the body and brain. Mental confusion, headaches, and more can be possible side effects of some treatments for MM.

Chemo brain,” which is a term for the brain fog and mental changes some people experience during chemotherapy, can affect people receiving the treatment for MM.

People experiencing unpleasant treatment side effects should contact a doctor.

Learn more about multiple myeloma treatment options.

MM symptoms can vary according to the stage of disease and the individual.

Initially, an individual may not know they have MM, and a doctor only discovers it following a routine blood or urine test.

As the disease progresses and individuals may experience various symptoms.

Bone problems

Bone problems can include bone pain and bone weakness. People experience pain primarily in the back, hips, and skull, although the pain may affect any bone.

Osteoporosis is when a person has fragile, low-density bones that break easily. It affects some people with MM.

Bone weakness may also occur if an individual has plasmacytoma. This condition is a form of cancer that begins in plasma cells and can turn into MM.

Low blood counts

People with MM commonly have shortages of white blood cells, red blood cells, and platelets. These shortages can lead to other symptoms.

A low red blood cell count causes anemia. People with anemia may have weakness, dizziness, and shortness of breath.

Doctors call a shortage of white blood cells leukopenia. Because white blood cells protect the body from harmful germs, someone with leukopenia has a lower resistance to infections.

A low platelet count is called thrombocytopenia. Because platelets help the blood clot, people with this condition may experience serious bleeding from small cuts or scratches.

Nervous system symptoms

Myeloma cells produce abnormal proteins. This may damage the nerves, resulting in numbness, weakness, and tingling.

Additionally, because MM can weaken the bones in the body, if this affects the bones of the spine, they may collapse and press on the spinal nerves. Doctors call this spinal cord compression.

If this happens, an individual may experience numbness in their legs, sudden severe back pain, and muscle weakness.

Doctors must treat spinal cord compression immediately in order to prevent possible paralysis.

People with multiple myeloma experiencing mental confusion symptoms should speak with a doctor.

Although these symptoms can be common in people with MM, they can be a result of various causes, some of which are more serious than others.

The doctor will likely perform a series of tests to determine the cause of the mental confusion and then treat the problem accordingly.

Mental confusion can be a symptom of multiple myeloma. It can be a result of blood hyperviscosity, high levels of calcium in the blood, or kidney issues.

Some treatments for MM, such as chemotherapy, can also cause mental confusion.

People with MM who experience mental confusion symptoms such as headache, brain fog, and loss of vision should contact a doctor. They can diagnose the cause and prescribe the appropriate treatment.