Abstract
Symptoms of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) can involve the central nervous system (cognition, executive function, short-term memory), the peripheral nervous system (muscle weakness, fatigue with exertion), and the autonomic nervous system (heart rate, blood pressure, breathing, digestion).
A close analysis of 177 symptom checklists collected from CFS/ME patients over 4.5 years revealed a previously unreported commonality among patients. The majority of patients present with some level of anticholinergic syndrome – a dramatic deficiency of acetylcholine, which could be responsible for symptoms affecting the central, peripheral and autonomic nervous systems. This is the first time that low acetylcholine levels have been suggested as a cause of many disabling symptoms in CFS/ME.
Prevalence estimates of Chronic Fatigue Syndrome range from 0.5% to 3% in the United States (2-9 million sufferers), and yet effective treatment continues to elude practitioners. A syndrome similar to Chronic Fatigue Syndrome has been described as far back as the mid-18th century[1], but the medical community struggles for consensus. Indeed, even the name Chronic Fatigue Syndrome is a point of contention. Chronic Fatigue Syndrome may be called systemic exertion intolerance disease (SEID), myalgic encephalomyelitis, chronic fatigue, and immune dysfunction syndrome, among others.[2] Currently, most sources use a combined term, Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) to describe this disorder.
| Frequency of Symptoms Occurring in Chronic Fatigue Syndrome | |
|---|---|
| Symptom | Percent of patients |
| Easily fatigued | 100 |
| Difficulty concentrating | 90 |
| Headache | 90 |
| Sore throat | 85 |
| Tender lymph nodes | 80 |
| Muscle aches | 80 |
| Joint aches | 75 |
| Feverishness | 75 |
| Difficulty sleeping | 70 |
| Psychiatric problems | 65 |
| Allergies | 55 |
| Abdominal cramps | 40 |
| Weight loss | 20 |
| Rash | 10 |
| Rapid pulse | 10 |
| Weight gain | 5 |
| Chest pain | 5 |
| Night sweats | 5 |
| Figure 1. Straus, SE, J Infect Dis 1988; 157:405.[3] |
Countless patients are clearly suffering from a constellation of debilitating symptoms, yet there is a frustrating lack of objective biomedical findings. As such, clinicians struggle to even make the diagnosis of CFS/ME much less provide effective treatment.
There is no “typical” presentation of CFS/ME, yet there are some features common to many patients with the syndrome. Most patients are high-functioning prior to illness and experience a sudden onset of symptoms, usually after a viral illness, trauma or extreme stress. Excessive physical activity exacerbates fatigue and related symptoms.
Many patients describe certain triggers that bring about or worsen symptoms such as emotional distress, physical trauma, decreased sleep quantity/quality, infection, and standing or sitting up for an extended period.[4] [5] [6] Each of these triggers taxes the patient and is, in one form or another, an exertion. Indeed, post-exertional malaise is often included as a diagnostic criterion. Post-exertional malaise is an exacerbation of some or all of an individual’s CFS/ME symptoms that occurs after physical or cognitive exertion and leads to a reduction in functional ability.[7] Exertion exacerbates fatigue, cognitive symptoms, pain, delayed recovery of muscle function, increased severity and incidence of sleep problems, and inappropriate autonomic responses.[4] [8] [9]
A large number of additional symptoms, beyond fatigue, are present in a majority of CFS/ME sufferers, and often, these symptoms can come and go. These symptoms can include sore throat, tender lymph nodes, muscle and joint pain, feverishness, insomnia, tachycardia, abdominal pain and others (see Figure 1). Attempts to locate the underlying cause(s) of such disparate symptoms have been unsuccessful to date. Some of the leading hypotheses are viral infection [3][10] , immune dysfunction[11], endocrine/metabolic dysfunction[12] [13], neurally – mediated hypotension[14] [15], genetic disorders[16] [17], disordered sleep[18], and complicated depression.[19]
Clearly, multiple systems of the body are involved simultaneously in CFS/ME. Symptoms of CSF/ME involve the central nervous system (cognition, executive function, short-term memory), the peripheral nervous system (muscle weakness, fatigue with exertion), and the autonomic nervous system (heart rate, blood pressure, breathing, digestion).
Central Nervous System in Chronic Fatigue Syndrome
The cognitive symptoms of CFS/ME can be every bit as debilitating as the physical symptoms. Patients report phenomena such as “brain fog,” confusion, and the inability to concentrate.[5] Short-term memory deficits and slowed information processing are common; the latter may be experienced as a mental fatigue similar to the physical fatigue of the condition.[20]
In CFS/ME, the prevalence of attention deficits may be as high as 93% and 85% for memory disturbances.[22] Three-quarters of patients experience substantial difficulty finding the correct words during verbal tasks.[22] Problems remembering, difficulty expressing thoughts, difficulty paying attention, slowness of thought, absentmindedness, and difficulty understanding are orders of magnitude more common in people with CFS/ME than in healthy volunteers.[23]
Peripheral Nervous System in Chronic Fatigue Syndrome
The peripheral nervous system (which controls muscles) has been found to affect CFS/ME patients and not uncommonly, patients complain of weakness. Fulcher, et al. found that patients with CFS/ME were weaker than sedentary and depressed controls, suggesting that weakness was not psychosomatic or secondary to deconditioning. Their study found that CFS/ME patients had significantly higher submaximal oxygen uptakes during exercise, and multiple regression models suggested that exercise incapacity was directly related to quadriceps muscle weakness.[24]
Autonomic Nervous System in Chronic Fatigue Syndrome
The autonomic nervous system controls bodily functions such as heart rate, blood pressure, pupil dilation, digestion, and salivation. It coordinates the activity of various organ systems without requiring conscious effort.
Many CSF/ME patients have abnormal autonomic nervous system function.[2]Orthostatic intolerance (the inability to adjust heart rate and blood pressure when changing position) is included in the updated diagnostic criteria for Chronic Fatigue Syndrome. Orthostatic intolerance includes symptoms of lightheadedness, dizziness, faintness, or syncope when vertical. Patients may present with neurally mediated hypotension, extreme pallor, nausea, irritable bowel syndrome, heart palpitations with or without cardiac arrhythmias, urinary frequency and bladder dysfunction, and exertional dyspnea and/or postural orthostatic tachycardia syndrome (POTS).[7][25]
What anomaly can tie together disorders of peripheral, central and autonomic nervous systems?
To look for clues to answer this question, between June 2011 and April 2015, Genetic Disease Investigators, LLC collected symptom questionnaires from 192 individuals with CFS/ME, resulting in 177 viable checklists. Each questionnaire contained 156 potential symptoms listed alphabetically.
Not surprisingly, autonomic symptoms were common. Percentage of respondents suffering with the following autonomic symptoms included:
| Symptom | % |
|---|---|
| Constipation | 89 |
| Difficulty breathing | 80 |
| Dry eyes | 78 |
| Dry mouth | 76 |
| Gastroparesis | 51 |
| Light sensitivity | 88 |
| Large pupils | 47 |
| Lack of perspiration | 46 |
| Decreased blood pressure when standing | 78 |
| Bradycardia or tachycardia | 81 |
| Increased body temperature | 57 |
| Urinary retention | 48 |
Central nervous system symptoms were also common. The percentage of respondents suffering with the following central nervous system symptoms included:
| Symptom | % |
|---|---|
| Agitation | 81 |
| Abnormal mood swings – almost bipolar presentation | 41 |
| Confusion | 81 |
| Disorientation | 79 |
| Illogical thinking | 55 |
| Difficulty concentrating | 79 |
| Memory problems | 89 |
| Brain fog | 96 |
| Easily startled | 80 |
| Irritability | 84 |
Peripheral nervous system symptoms were also common and were reported with the following frequency:
| Symptom | % |
|---|---|
| Extreme fatigue | 100 |
| Tremor | 69 |
| Shaking | 70 |
| Wakeful myoclonic jerks | 74 |
| Loss of coordination (ataxia) | 77 |
Additional symptoms not currently regarded as typical for CSF/ME (yet often present in anticholinergic syndrome) were reported with the following frequency:
| Symptom | % |
|---|---|
| Seeing periodic flashes of light | 63 |
| Seeing “dancing lines, spiders or insects” | 42 |
| Double vision | 67 |
| Hallucinations – auditory or visual | 28 |
| Textured surfaces bother you visually | 45 |
| Tunnel vision | 36 |
| Visual snow | 54 |
| Warping or waving of surfaces and edges | 29 |
| Sensitivity to sudden sounds | 96 |
When viewed as a whole, the above 36 symptoms are the symptoms of Acute Anticholinergic Syndrome. This syndrome must be identified by presentation (not via blood work) because acetylcholine breaks down rapidly. These symptoms suggest, but do not prove, that the majority of patients with CFS/ME suffer from symptoms of extremely low levels of acetylcholine.
Could CSF/ME patients be suffering with extremely low levels of the neurotransmitter, acetylcholine, resulting in symptoms involving the peripheral, central, and autonomic nervous system?
The actions of acetylcholine in the central, peripheral, and autonomic nervous systems
To understand abnormalities in acetylcholine, one must first understand where and how it acts under normal circumstances. Acetylcholine is the neurotransmitter of neuromuscular junctions, ganglia in the autonomic nervous system, and is present in discrete locations throughout the brain.[26]
In the central nervous system (the brain and spinal cord), acetylcholine is critical for memory formation and recall. For example, there are acetylcholine receptors in the hippocampus, neocortex, and amygdala — the main memory-forming structures in the brain.[27] Likewise, acetylcholine is the major neurotransmitter in the basal nucleus of Meynert, which degenerates in Alzheimer’s disease.[28]
Acetylcholine is integral to the proper function of the peripheral nervous system and is the main neurotransmitter at every skeletal neuromuscular junction in the body. All conscious muscular movement requires acetylcholine.
Acetylcholine is a major component of the autonomic nervous system and is required for proper vagus nerve function.
Acetylcholine and Chronic Fatigue Syndrome
As a syndrome, CFS/ME is a constellation of symptoms. It is difficult to envision a single pathological process that gives rise to all of the various symptoms. Nevertheless, abnormalities in the acetylcholine system could explain many, if not most of the symptoms of CFS/ME.
The effects of acetylcholine deficiency are understood primarily because of the actions of atropine. Atropine blocks acetylcholine receptors, thus preventing the neurotransmitter from interacting with postsynaptic neurons. Acetylcholine deficiency (brought on by atropine) causes ventricular fibrillation, tachycardia (rapid heart rate), dizziness, nausea, blurred vision, loss of balance, dilated pupils, photophobia, dry mouth, dry eyes, extreme confusion, dissociative hallucinations, and excitation in addition to unusual symptoms such as visual snow and seeing “dancing lines, spiders and insects.”[29] [30]
The link between CFS/ME and acetylcholine has been the subject of ongoing research with particular attention to potential autoimmune conditions that could affect acetylcholine receptors. For example, some researchers found autoantibodies against muscarinic cholinergic receptors in over half of people with CFS/ME.[31] [32]
Spence, Khan, and Belch showed that patients with CFS/ME have abnormalities in the acetylcholine (cholinergic) system.[33] The researchers showed the acetylcholinesterase inhibitor, edrophonium, applied to the skin reacts abnormally in patients with chronic fatigue syndrome. The same research group has confirmed the results of their research in several papers.[34] [35] [36] [37]
Yamamoto et al. (2012) used a radioactive agent that specifically binds to muscarinic acetylcholine receptors in the brain. They report decreased levels of receptors in the brain, but normal activity of acetylcholinesterase.[38]
Taken together, these results suggest an interesting possibility that explains the disparate findings of all of these researchers: CFS/ME patients may have abnormally low levels of acetylcholine.
Could CFS/ME patients improve by boosting levels of acetylcholine?
If this hypothesis was true, one could treat many symptoms of chronic fatigue syndrome by increasing acetylcholine levels within the synapse. Indeed, researchers have attempted to do this very thing. Kawamura and co-authors report three cases in which a small dose of oral pyridostigmine, an acetylcholinesterase inhibitor that increases acetylcholine levels in synapses, improved symptoms of chronic fatigue syndrome.[39] Many patients with POTS (Postural Orthostatic Tachycardia Syndrome) have improved gastrointestinal symptoms (gastroparesis, constipation) with the use of pyridostigmine.[40]
But because pyridostigmine does not cross the blood-brain barrier, it cannot boost acetylcholine in the brain and assist with central nervous system symptoms.
Acting on the evidence of low acetylcholine levels as exhibited by symptomatology, Genetic Disease Investigators, LLC began to search for a compound that could cross the blood-brain barrier and boost acetylcholine in the central nervous system as well as effectively replace acetylcholine in the autonomic nervous system and the peripheral nervous system.
References
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