Diffuse midline glioma (DMG) is a rare form of brain tumor that mostly occurs in children and young adults. It can be highly aggressive and difficult to treat.

DMGs form within the central nervous system (CNS), which includes the brain and spinal cord.

These tumors are malignant, or cancerous, and fast-growing. This means they may spread quickly to other parts of the CNS.

This article explores DMG in more detail, including its symptoms, causes, diagnosis, treatment, and outlook.

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DMGs are a rare form of tumor that affect the CNS. According to the National Cancer Institute (NCI), they mainly form in these areas:

  • the thalamus, a structure in the center of the brain that relays sensory information from other parts of the body
  • the spinal cord
  • the cerebellum, part of the brain located at the base of the skull that helps coordinate movement and balance
  • the pons, which is located at the top of the brain stem and transmits information between parts of the brain

The tumors form from glial cells, which help to support and protect nerve cells. DMGs develop when mutations in these cells cause them to multiply uncontrollably.

Healthcare professionals use cancer grading to determine how far and fast cancer cells have spread in the body. Cancer grading typically uses a scale between 1 and 4. All DMG tumors are grade 4. This means they are malignant and fast-growing. Over time, they may spread to other areas of the CNS.

DMGs can affect both children and adults. However, they more commonly occur in younger people. The NCI notes that DMGs are most common in older children and young adults between the ages of 15 and 39. It also states that DMG is most common in non-Hispanic white people.

Additionally, a review of research from 2023 notes that DMGs account for 4 in 5 brainstem tumors in children.

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The NCI states that the exact cause of DMG is currently unknown. It notes that cancers occur due to mutations in genes that cause cells to multiply and spread.

Researchers believe that certain genetic conditions may increase a person’s risk of developing DMG. These include conditions that can pass down through families, such as Li-Fraumeni syndrome and neurofibromatosis type 1.

Additionally, changes in the gene h3K27M may also have links to DMG.

Symptoms of DMG may vary depending on where it develops. Possible symptoms include:

If a person has a DMG in their spine, they may experience symptoms such as:

  • numbness
  • progressive weakness
  • bladder or bowel control issues

DMGs may also cause an overproduction or blockage of cerebrospinal fluid (CSF), which is a clear fluid that surrounds the brain and spinal cord.

An increase in CSF or a CSF blockage may cause pressure to build inside the skull. This is known as hydrocephalus. It may cause symptoms such as:

A review from 2023 states that doctors generally diagnose DMG by evaluating a person’s symptoms and conducting MRI scans. A healthcare professional may also request a PET scan.

A doctor can also request a biopsy of the tumor, as imaging test results alone are not enough to confirm a DMG diagnosis. A biopsy involves a doctor taking a sample of tissue from the tumor. Once a doctor has taken a biopsy of the tumor, they can study it at a molecular level. This may help them determine the best course of treatment.

The NCI notes that, where possible, surgery is generally the first treatment for DMG. During surgery, a surgeon may take a biopsy of the tumor and remove as much as possible.

However, surgery can also affect the areas of the brain that DMG affects, potentially resulting in severe loss of function.

Additionally, DMG tumors are diffuse, meaning they do not have well-defined edges, and may grow into healthy tissue. This means that it can be difficult for a surgeon to remove the tumor successfully.

If surgery is too risky, a healthcare professional may treat a person’s DMG using radiation therapy.

A person will generally require additional treatments after they have surgery for DMG. These may include radiation therapy or chemotherapy. Healthcare professionals will speak with a person about what treatments are most suitable for them.

The NCI states that in general, the 5-year survival rate for DMG is 42.2%.

However, each individual outlook for DMG depends on several variables, such as:

  • the location of the tumor
  • the extent of the spread
  • genetic findings
  • a person’s age and overall health
  • the tumor’s molecular type
  • response to treatment
  • the amount of tumor left in the body after surgery if a person has been able to have it

Therefore, some individuals may have a more favorable outlook than average survival rates suggest.

A review from 2023 notes that people who have DMG with certain genetic mutations have a worse outlook than those without.

DMG is a rare type of CNS tumor that is more common in children and young adults. It is a malignant and fast-growing cancer. Over time, it may spread to other parts of the CNS.

The exact cause of DMG is unknown. However, researchers believe it may have links to certain genetic conditions.

DMG may cause different symptoms depending on what part of the CNS it has developed in and these can include double vision, weakness, and loss of balance.

Doctors generally diagnose DMG by evaluating a person’s symptoms and using imaging tests. They may also request a biopsy.

Healthcare professionals treat DMG with surgery if possible. They may also treat a person using radiation therapy or chemotherapy. The outlook depends on various individual factors. A person should speak with their doctor about their individual outlook.