1. Marked, rapid physical and/or cognitive fatigability in response to exertion, which may be minimal such as activities of daily living or simple mental tasks, can be debilitating and cause a relapse.
2. Post-exertional symptom exacerbation: e.g. acute flu-like symptoms, pain and worsening of other symptoms.
3. Post-exertional exhaustion may occur immediately after activity or be delayed by hours or days.
4. Recovery period is prolonged, usually taking 24 hours or longer. A relapse can last days, weeks or longer.
5. Low threshold of physical and mental fatigability (lack of stamina) results in a substantial reduction in pre-illness activity level.
B. Neurological Impairments
At least one symptom from three of the following four symptom categories:
1. Neurocognitive Impairments
a. Difficulty processing information: slowed thought, impaired concentration e.g. confusion, disorientation, cognitive overload, difficulty with making decisions, slowed speech, acquired or exertional dyslexia.
b. Short-term memory loss: e.g. difficulty remembering what one wanted to say, what one was saying, retrieving words, recalling information, poor working memory.
a. Headaches: e.g. chronic, generalized headaches often involve aching of the eyes, behind the eyes or back of the head that may be associated with cervical muscle tension; migraine; tension headaches .
b. Significant pain can be experienced in muscles, muscle-tendon junctions, joints, abdomen or chest. It is non-inflammatory in nature and often migrates. e.g. generalized hyperalgesia, widespread pain
(may meet fibromyalgia criteria), myofascial or radiating pain.
3. Sleep Disturbance
a. Disturbed sleep patterns: e.g. insomnia, prolonged sleep including naps, sleeping most of the day and being awake most of the night, frequent awakenings, awaking much earlier than before illness onset, vivid dreams/nightmares.
b. Unrefreshed sleep: e.g. awaken feeling exhausted regardless of duration of sleep, day-time sleepiness
4. Neurosensory, Perceptual and Motor Disturbances
a. Neurosensory and perceptual: e.g. inability to focus vision, sensitivity to light, noise, vibration, odour, taste and touch; impaired depth perception.
b. Motor: e.g. muscle weakness, twitching, poor coordination, feeling unsteady on feet, ataxia.
C. Immune, Gastro-intestinal & Genitourinary Impairments
At least one symptom from three of the following five symptom categories:
1. Flu-like symptoms may be recurrent or chronic and typically activate or worsen with exertion. e.g. sore throat, sinusitis, cervical and/or axillary lymph nodes may enlarge or be tender on palpitation.
2. Susceptibility to viral infections with prolonged recovery periods.
3. Gastro-intestinal tract: e.g. nausea, abdominal pain, bloating, irritable bowel syndrome.
4. Genitourinary: e.g. urinary urgency or frequency, nocturia.
5. Sensitivities to food, medications, odours or chemicals
D. Energy Production/Transportation Impairments
At least one symptom:
1. Cardiovascular: e.g. inability to tolerate an upright position – orthostatic intolerance, neurally mediated hypotension, postural orthostatic tachycardia syndrome, palpitations with or without cardiac arrhythmias, light-headedness/dizziness.
2. Respiratory: e.g. air hunger, laboured breathing, fatigue of chest wall muscles.
3. Loss of thermostatic stability: e.g. subnormal body temperature, marked diurnal fluctuations; sweating episodes, recurrent feelings of feverishness with or without low grade fever, cold extremities.
4. Intolerance of extremes of temperature.
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