What causes autonomic disorders?
There are certain underlying conditions that can predispose to the development of problems with the autonomic nervous system.
Diabetes- When sugars run too high they can be toxic to nerves including autonomic nerves. Just as described in the neuropathy page when diabetes affects the nerves it affects the longest ones first. In the case of the autonomic nervous system the longest nerve is the “vagus” nerve. This nerve forms a large part of the parasympathetic (or rest and digest) side of the autonomic nervous system. When this nerve is damaged the first sign is a fast resting heart rate. This also manifests as poor heart rate variability. As these symptoms progress they will eventually lead to all the symptoms described under cardiovascular symptoms above. It is when these are beginning to develop that action can be taken to reverse or at the very least stop progression of the nerve damage. Diabetes also affects all the other aspects of the autonomic nervous system and any of the symptoms described above can result from poorly controlled diabetes.
Parkinson’s disease (PD)- can be associated with autonomic problems. In PD there is degeneration of nerve cells in the brain that are responsible for the production of a neurotransmitter called dopamine- it is dopamine that allows us to have smooth controlled movements (see Parkinson’s disease page). There is also denervation of autonomic nerves especially those that are providing a nerve supply to the heart- primarily those nerves of the sympathetic (or fight-or-flight) side of the autonomic nervous system. This translates into an inability of the heart to increase the heart rate in response to a demanding task. This tends to manifest as orthostatic hypotension (described above) where there is a drop in blood pressure on standing that cannot be compensated for by increasing the heart rate. Patients with PD often suffer from sleep related problems one of which is the rapid eye movement (REM) sleep behaviour disorder (described on the Parkinson’s disease page). There are studies that demonstrate a link between dysfunction of the autonomic nervous system and this sleep disorder. Further to that, when the autonomic nerve supply to the bladder becomes involved this leads to interruption of sleep from having to get up to go to the toilet during the night. This can then lead to daytime sleepiness. For some (largely unknown) reason in PD the autonomic nerves that are the most affected are the sympathetic nerves supplying the heart. There is another condition that is related to PD but has distinctive features. This condition is called multiple system atrophy (MSA) (described on Parkinson’s disease page) that is also associated with autonomic dysfunction.
Hereditary autonomic neuropathy- There are several different types of inherited diseases that can cause autonomic nerve dysfunction. These often cause problems also with sensory nerves as both (sensory and autonomic) of these types of nerves are small and in hereditary conditions they may be affected together. These are collectively referred to as “hereditary sensory and autonomic neuropathies” and there are several types and several different genetic mutations responsible. The one that is also referred to as “familial dysautonomia” tends to predominantly affect the autonomic nervous system but the others tend to have more sensory involvement. It should be noted that even though there are several of these conditions described they are incredibly rare.
Pure Autonomic Failure (PAF)- This is a relatively recently described disorder in which there is a progressive degeneration of the nerves of the autonomic nervous system. It is a rare and very slowly progressive condition. It tends to present in middle to later life and it affects men more than women. The most common presenting symptom is lightheadedness or unsteadiness on standing up because of orthostatic hypotension (described above). In men impotence is often an early symptom of PAF. The most important thing in diagnosing someone with PAF is to ensure there are no signs suggesting an alternative condition such as PD- but this is the job for your neurologist!
Vitamin B12 deficiency- Nutritional deficiencies such as deficiency in vitamins B12 have been found in patients with autonomic dysfunction. It appears to have the greatest effect on the sympathetic component of the autonomic nervous system and has been likened to the type of autonomic dysfunction that occurs in patients with diabetes.
Toxicity- from either alcohol or chemotherapy drugs can lead to autonomic dysfunction in much the same way as they can affect small nerves responsible for sensation.
Auto-immune disorders- There is an auto-immune condition that can lead to autonomic nervous system dysfunction. Autoimmune means that your own body has formed antibodies against a certain part of your own system. Often it occurs in conjunction with an infection such as a gastrointestinal illness. When your immune system attacks the infection it does this through the formation of antibodies. The antibodies are attacking the infection however sometimes they get mixed up and also attack certain parts of the nerve. In an auto-immune autonomic neuropathy the antibody attacks the autonomic nerves leading to a constellation of the symptoms described above.