What is dysautonomia?
Dysautonomia is the medical term for a malfunctioning autonomic nervous system (ANS). The ANS controls the automatic functions of the body to keep it in balance. It responds to stressors such as physical exertion, position changes, cold, heat, and strong emotions.
There are many autonomic functions in addition to the examples listed below. The severity of dysautonomia symptoms varies widely. Many Sjogren’s patients have subclinical manifestations that can be measured but have no obvious symptoms. On the other hand, dysautonomias may be severe and disabling.
EXAMPLES OF THE AUTONOMIC NERVOUS SYSTEM FUNCTIONS:
Blood pressure, heart rate, and blood vessels adjust automatically to respond to body position changes, exertion, emotional events, etc.
Sweating: stimulated by heat and emotional states
Pupils: contract in bright light and dilate in the dark.
Gut motility: stimulated by eating.
Cardiovascular dysautonomias impact the heart rate, blood pressure, and the blood vessels. The blood vessels have tiny little muscles on their outer walls that automatically squeeze down in response to sitting up or standing. This squeezing action helps keep the blood from pooling in the lower half of the body. In Postural Orthostatic Tachycardia Syndrome (POTS), this adjustment by the blood vessels to upright posture does not work well. POTS is one of the most common cardiovascular dysautonomias.
Orthostatic Intolerance (OI) is the inability to tolerate upright posture, especially prolonged standing. Chronic OI is usually caused by some type of cardiovascular dysautonomia. OI is usually associated with lightheadedness, brain fog, fatigue, feeling tremulous, headaches/ migraine, and sometimes shortness of breath. Many who have OI also have tachycardia (rapid heart rate). Other conditions such as dehydration my cause temporary OI.
Small Fiber Neuropathy (SFN) refers to damage of the unmyelinated or thinly myelinated tiny nerves of the peripheral nervous system. SFN often impacts the pain nerve fibers, especially in the feet, although it can occur in other parts of the body. Temperature, light touch and other sensations may also be impacted by SFN.
Dysautonomia and SFN have a lot in common.
Dysautonomias are usually caused by damage to the small nerve fibers controlling the ANS, although they sometimes arise from other places in the nervous system. Sensory small fiber neuropathies and dysautonomia are the most common neurologic features in Sjogren’s (151, Ch. 9).
SFN and dysautonomias cannot be detected by nerve conduction studies (NCS), which only pick up abnormalities in the large myelinated nerves.
Dysautonomia and sensory SFN often occur together.
Sjogren’s patients may have any mix of SFN, dysautonomia, and large fiber neuropathy (LFN). Although LFN is the least common of the three, many clinicians and Sjogren’s researchers focus on LFN because it can be verified by routine neurologic examination and NCS. Large fiber neuropathies may impact both motor (muscle) and sensory function. These may present dramatically with a loss of muscle function in a limb or difficulty balancing when walking (151, Ch. 9).
Despite being common in Sjogren’s patients, dysautonomia is often overlooked due to lack of clinician awareness and training. All too often, it is labeled as anxiety or functional neurologic disorder.
Are there tests for small fiber neuropathy and dysautonomia?
These conditions may be confirmed by specialized tests such as skin biopsy, tilt table testing, QSART, and others. Even these tests are not 100 % accurate. Most neurology clinics are not set up to perform autonomic testing (32, 33).
Dysautonomia remains vastly underdiagnosed in Sjogren’s. It probably contributes significantly to the most distressing symptoms reported by Sjogren’s patients: Fatigue, brain fog, heat intolerance, swallowing problems, and abnormal stomach and intestinal motility.
More research is needed to understand these conditions and find better treatments. Rheumatologists and neurologists need to be trained to recognize, diagnose and manage these conditions.