Diffuse midline gliomas (DMG) are a rare and aggressive type of cancer that develops from glial (or supportive) tissue in the brain, which supports and protects the brains neurons. They develop within the midline structures of the body, including the brainstem, spinal cord, and thalamus, and most commonly affect children.
The brain is a complex organ that is responsible for controlling all functions of the body. It has five main portions: the cerebrum, cerebellum, brainstem, pituitary gland, and hypothalamus. The cerebrum is the biggest part of the brain, and consists of the frontal, parietal, temporal, and occipital lobes. This part of the brain is responsible for voluntary movement, intelligence, and memory. The cerebellum is a small part of the brain located at the back of the head, and regulates posture and balance. The brainstem is a small, stalk-like structure towards the bottom of the brain that connects the brain to the spinal cord. It is divided into three sections: the midbrain (or mesencephalon), pons (or metencephalon), and medulla (or medulla oblongata). Each component of the brainstem works together to control and regulate vital bodily functions, such as breathing, heart rate, blood pressure, as well as the nerves and muscles used for seeing, hearing, walking, talking, and eating. The pituitary gland is a pea sized organ located behind the eyes, and is responsible for the production and secretion of hormones in the body. The hypothalamus is located deep within the brain, and has many important functions, such as producing and secreting different hormones, regulating temperature, and controlling appetite.
The spinal cord is a long, thin, tubular structure that extends down from the brainstem to the lower back. It is made of nerve tissue, and is surrounded by the bones of the spine (vertebrae). The spinal cord is responsible for transmitting nerve signals from the brain to the body, and vice versa. It has motor functions (such as voluntary movement), sensory functions (such as pressure, touch, temperature, and pain), and autonomous functions (such as regulating digestion, heart rate, and blood pressure).
DMGs and diffuse intrinsic pontine gliomas (DIPGs) are often classified together, but can have different treatment options. For more information on DIPG, please refer to the Rare Cancers Australia Diffuse Intrinsic Pontine Glioma (DIPG) page.
DMGs are slightly more common in males, and are most commonly diagnosed between the ages of five and seven. However, anyone can develop this disease.
Treatment
When cancers are detected, they are staged and graded based on size, metastasis (whether the cancer has spread to other parts of the body), and how the cancer cells look under the microscope. Staging and grading helps your doctors determine the best treatment for you. However, brain cancers are rarely staged, as they rarely spread to other parts of the body. Instead, they are generally graded from I-IV.
DMGs are considered to be grade IV tumours, as the tumour cells appear very abnormal under the microscope and grow rapidly.
Your doctor may also recommend genetic testing, which analyses your tumour DNA and can help determine which treatment has the greatest chance of success. They will then discuss the most appropriate treatment option for you.
Treatment is dependent on several factors, including location, age, and overall health.
Treatment options form DMG may include:
- Surgery to remove as much of the tumour as possible (if possible – dependent on tumour location).
- Radiation therapy.
- Experimental chemotherapy.
- Steroids.
- Insertion of a stent to relieve a build-up of cerebrospinal fluid (CSF) in the brain.
- Clinical trials.
- Palliative care.
For more information on the treatment options, please refer to the Rare Cancers Australia treatment options page.
Clinical Trials for DMG
Clinical trials are research studies performed to test new treatments. They present the opportunity for people, particularly those with rare or complex cancers such as DMG, to receive very new treatments which are not yet available otherwise. While these studies have the potential to develop more treatment options, the risk of side effects can be high and are not always known.
Ask your doctors about the availability of clinical trials and whether your child is suitable, as well as any benefits, risks and potential complications that may arise.
Risk factors
Because of how rare DMG is, there has been limited research done into the risk factors of this disease. However, some recent research has suggested that there is a potential link to abnormal brain development and certain genetic and epigenetic mutations.
Early symptoms
In most cases, the onset of symptoms occurs very rapidly before diagnosis, reflecting the fast growth of DMG tumours. Because of the aggressive nature of these tumours and their growth rate, symptoms generally progress very quickly.
Common symptoms of DMG include:
- Problems controlling eye movement, facial expressions, chewing and/or swallowing (as a result of nerve compression in the brain).
- Slurred speech.
- Difficulties with balance.
- Hydrocephalus (fluid build-up in the brain).
- Headaches (often after waking up in the morning).
- Nausea and/or vomiting (generally worse in the morning).
- Irritability.
- Blurred or double vision.
- Seizures.
- Lethargy (lack of energy).
- Fatigue.
- Changes in eating habits/appetite.
- Difficulty walking.
- Personality changes.
- Enlarged fontanelles (soft spots on an infant's head between the bony plates of the skull).
- Enlarged head (more common in infants).
- Facial drooping.
- Difficulties urinating and/or with bowel movements.
- Weakness and/or numbness in the arms and/or the legs.
- Clumsiness.
Not everyone with the symptoms above will have cancer, but see your general practitioner (GP) if you are concerned.
Diagnosis/diagnosing
If your doctor suspects you have a DMG, they may order the following tests to confirm the diagnosis and refer you to a specialist for treatment.
Imaging & Blood tests
The doctor will take images of your body using magnetic resonance imaging (MRI), a computed tomography scan (CT scan), x-rays and/or positron emission tomography (PET scan), depending on where it is suspected the cancer is. The doctor may also look at other parts of the body and look for signs of metastasis. Additionally, a blood test may be taken to assess your overall health and help guide treatment decisions.
Physical examination
Your doctor will collect your overall medical history, as well as your current symptoms. Following this, they may examine your body to check for any abnormalities.
Neurological examination
A neurological examination assesses sensory and motor functions, and can generally be done in your GPs office. The doctor may check your vision, hearing, balance, coordination, strength, and reflexes, depending on the signs and symptoms you have described. Any problem that is detected in this exam can help determine which portion of the CNS needs further investigation.
Biopsy
Once the location of the cancer has been identified, the doctor may perform a biopsy to remove a section of tissue using a needle. This sample will then be sent to the lab and analysed for cancer cells.
Because of the tumour location and its diffuse nature, biopsies are not always performed in patients who are suspected to have a DMG. In many cases, a diagnosis can be given based on other tests.
Prognosis (Certain factors affect the prognosis and treatment options)
Unfortunately, the prognosis for DMG remains very poor. Brain tumours remain the most common cause of cancer-related death in children, and DMG and DIPG are the leading cause of death from paediatric brain tumours. It is very important to discuss your individual circumstances with your doctor to better understand your prognosis.
References
Some references are to overseas websites. There may be references to drugs and clinical trials that are not available here in Australia.