Balance is the result of the brain integrating three separate senses:
- Proprioception (sense of body position)
NF2 most characteristically impacts the vestibular sense, but can certainly affect the other two as well. Normally, sight and proprioception can compensate for loss of vestibular function to a degree, but situations that impair these two other senses can severely degrade balance. This is why it is so dangerous for many with NF2 to swim underwater, since the inability to visualize a horizontal reference plane eliminates useful visual input, and buoyancy confuses proprioception.
Many with NF2 have impaired vision, not just from garden-variety refractive errors, but from corneal damage from dry eye. Some also have neurological visual deficits due to optic chiasm tumors.
Proprioception is a function that is largely shared by two systems – the conscious sensory input from pressure and tension receptors in the joints, tendons, and muscles, and the unconscious participation of the cerebellum. All these systems interact with the muscles to maintain adequate support against forces that would otherwise topple us over. Unfortunately, the system can become disrupted at almost any point – from the peripheral sensory nerves, to the spinal nerve tracts, to the brainstem, thalamus, sensory cortex, motor cortex, and down through the upper motor tracts and spinal motor nerves. Peripheral neuropathy (such as seen in diabetes or certain drug therapies) could block proprioceptive input almost at its beginning; a spinal tumor could compress either the ascending dorsal nerve tracts or the spinocerebellar tract, or even the descending motor tracts, causing subtle muscular deficits. And almost everyone who has had a retrosigmoid acoustic neuroma surgery has significant damage to his or her cerebellum.
Not all balance difficulties can be treated, but if yours can be correlated with a discreet lesion- for example, a spinal tumor – this would suggest a way to manage it. Failing that, there are techniques aimed at improving balance – physical therapists use techniques that many surgeons are unaware of, such as sensory integration or vestibular therapy. If the problem is causing sufficient difficulty, you should consider investigating strategies that are outside the surgeon’s “sphere of influence”.
Cerebellum: Balance & Coordination
The Cerebellum is involved in the coordination of voluntary motor movement, BALANCE and equilibrium and muscle tone. It is located just above the brain stem and toward the back of the brain. It is relatively well protected from trauma compared to the frontal and temporal lobes and brain stem.
Cerebellar injury caused by tumors results in movements that are slow and uncoordinated. Individuals with cerebellar lesions tend to sway and stagger when walking.1
Damage to the Cerebellum can lead to:
- loss of coordination of motor movement (asynergia)
- the inability to judge distance and when to stop (dysmetria)
- the inability to perform rapid alternating movements (adiadochokinesia)
- movement tremors (intention tremor)
- staggering, wide based walking (ataxic gait)
- tendency toward falling
- weak muscles (hypotonia)
- slurred speech (ataxic dysarthria)
- abnormal eye movements (nystagmus).” 1
1 Cerebellum – Traumatic Brain Injury (TBI)
- Balance Disorders
- Movement – uncoordinated
- Balance and Dizziness – Mass. Eye and Ear is one of the few hospitals in the world with experts and facilities specifically devoted to investigating and treating issues of balance and dizziness.
- Cerebellar Vermis
- Tilt determination in MEMS inertial vestibular prosthesis. – PubMed
- The balance control of bilateral peripheral vestibular loss subjects and its improvement with auditory prosthetic feedback. – PubMed
- Vestibular Disorders Association
- Maintaining Balance With Age
- Balance Disorders: a common, complex problem
- Vertigo Overview, Incidence & Prevalence