Reflex tests are part of the neurological examination given by a doctor when checking for a brain tumour. Doctors use various reflex tests to determine whether the nerve pathways travelling to the brain from elsewhere in the body are damaged. If there is pressure on one or more nerves by a brain tumour, the nervous system will not properly respond to the reflex tests.
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Reflexes are the body's automatic response to a stimulus. When the body's systems are functioning properly, a doctor would expect certain reflexes from the body once it receives a stimulus. The significance of a reflex is that it will tell a doctor whether a nerve pathway is functioning normally or abnormally. If the nerve pathways are damaged, the body will not react with the proper response, and this allows for further investigation into the brain. Reflex tests may include the blink reflex, pupil dilation after shining a light into the eye, oral reflexes and rubber hammer tests of the knees because these are some of the most common reflexes affected by a brain tumour. The tests do not have to be performed in a certain order.
Blink Diagnostic Test
A study of the blink reflex can reveal disorders that affect nerves in the head and neck as well as brainstem function. During this test, small electrodes are attached to the skin around the eyes and nose. The doctor will administer mild electrical impulses to the nerves and record the blinking responses. These can be mildly or moderately uncomfortable. The doctor is studying the blink reflex to see if the blink happens as expected when the impulses are administered. A missing blink can indicate nerve damage.
If a brain tumour has formed in an area that affects the nerves in the brain, it will cause uneven pupil dilation, even at times when the eyes are not stimulated by light. A tumour can affect the brain's pathways and cause abnormal reactions from the retina and the optic nerve.This causes the pupils to appear larger than normal. Although it is rarely the single symptom for a brain tumour, it is something that causes a doctor to investigate further.
Brainstem gliomas, which are brain tumours located on the brainstem, cause difficulty in swallowing and, at times, an absent gag reflex. A doctor will lightly brush the posterior pharynx and determine whether the patient gags. If the patient does not gag, the reflex is said to be absent.
Gliomas can also cause trouble with movement of the tongue. Although the patient may attempt to move the tongue to the right side of the mouth, it moves to the left, or vice-versa.
Rubber hammer tests are performed throughout the body in places like the knees. A tap on the tendon below the kneecap with a rubber hammer should cause the lower leg to jump. However, with a brain tumour, the nerve pathways can be damaged and the proper reaction is absent many times. Similar reactions are expected at the elbows and ankles.
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