This is a frequent symptom which may be defined as:- "decreased muscle strength compared to perceived effort"
When neurological weakness is suspected, the first thing a neurologist will ascertain is whether the complaint is of "general weakness or fatigue" rather than real muscle weakness which usually occurs in specific areas of the body or certain muscle groups.
"General fatigue" is not a specific complaint.
Although it can sometimes signify a diffuse (widespread) neurological condition, it is more commonly due to other conditions not considered to be "neurological" in the classical sense.
Such situations include,depression,"chronic fatigue syndrome" a general "internal medical" illness of any kind (eg.infections, liver or kidney problems, biochemical or hormonal imbalance, and even simple sleep deprivation to name but a few.
Neurological Muscle Weakness
In general,this type of problem preferentially affects some areas and not others.
Some conditions can ultimately deteriorate to severe lack of strength of the whole body (eg
AIDP / Guillan Barre syndrome, myasthenia gravis
However at the initial stages of the condition, the condition will almost invariably affect some areas whilst "sparing" others.
Systematic approach to diagnosing the site of the neurological weakness
e.g. "decreased leg strength"
Starting from the brain and moving down and out (proximal to distal) a problem in the following components can adversely affect leg strength:-
1) Brain (e.g.primary motor area of cerebral cortex)
2) Spinal cord
3) Nerve roots
5) Neuromuscular junction (where the nerve meets and transmits messages to the muscle)
It is only after a neurologist decides "where the lesion is" that they move on to investigate "what is the cause of the lesion"
For example...someone who has a problem walking due to weak legs may be diagnosed with a spinal cord problem that may ultimately be found to be due to
MS (multiple sclerosis).
Does twitching indicate neurological weakness?