Muscle weakness is an extremely common chief complaint that affects millions of people across the globe. However, most people confuse muscle weakness with fatigue or lethargy.

From a medical perspective, weakness describes the loss of muscle strength due to an injury in the nerve, neuromuscular junction, or the muscle fibers themselves. This disorder could affect one muscle or an entire group of muscles.

When the weakness affects certain muscle groups, you could experience eye movement abnormalities, dysphagia (i.e., difficulty swallowing), dysarthria (i.e., inability to speak), and respiratory insufficiency.

Understandably, when patients see their neurologist, they often do not know the difference between muscle weakness and fatigue. In reality, the two terms are dissimilar and have completely different causes.

  • Weakness describes the inability to perform regular physical activities due to the loss of muscle strength.
  • Fatigue is a feeling of exhaustion because of a lack of energy. It could result from overwork, excessive stress, poor sleep quality, lack of exercise, or boredom. Fatigue is more common than muscle weakness as hundreds of medical conditions and medications can cause it.

It is worth noting that both weakness and fatigue are symptoms, not diseases. In other words, your neurologist will conduct a thorough investigation to pinpoint the underlying cause that is triggering your symptoms.

The causes of muscle weakness are extremely diverse. For this reason, you will need the knowledge and expertise of a neurologist to diagnose it.

Here is a shortlist of some of these causes:

  • Neurologic disorders (e.g., spinal cord injury, amyotrophic lateral sclerosis, stroke, multiple sclerosis, botulism, myasthenia gravis)
  • Infections (e.g., Epstein-Barr virus, HIV, Lyme disease, Polio, Rabies)
  • Drugs (e.g., alcohol)
  • Endocrine disorders (e.g., adrenal insufficiency)
  • Inflammatory disorders (e.g., dermatomyositis, inclusion body myositis, polymyositis)
  • Electrolytes imbalances (e.g., hypercalcemia, hypokalemia, hypermagnesemia)

In elderly individuals, strokes are the most common cause of weakness disorders.

A stroke occurs when blood cannot reach a specific area of the brain due to arterial rupture or clogging of the blood vessel.

As a result, oxygen and nutrients can no longer reach brain cells (i.e., neurons), leading to tissue death.

According to the Centers for Disease Control and Prevention (CDC), stroke is number 5 on the list of most deadly diseases in the United States. This translates to more than 795,000 stroke cases every year.

Generally speaking, there are two types of stroke:

Ischemic stroke –results from the blockage of an artery that irrigates an important area of the brain.

Hemorrhagic stroke –results from the rupture of an artery and bleeding surrounding brain tissue.

To diagnose a weakness disorder, your neurologist will gather as much information as possible.

The first step revolves around your medical history. This is perhaps the most important step of diagnosing weakness. Your neurologist will ask you about your medical history, which includes the following questions:

  • Do you have any current illnesses?
  • What diseases/infections did you develop in the past?
  • Are you taking any medications?
  • Are there any neurological disorders that run in your family?
  • Do you have any other symptoms besides weakness?
  • Are you experiencing any pain?
  • How muscle weakness is impacting your daily life?

After gathering the necessary information from your medical history, it is time for the physical examination. Your neurologist will conduct a comprehensive physical exam that includes checking your reflexes and assessing muscle strength/size.

Using a measuring tape, he/she will compare the size of your muscles on both sides. For instance, the neurologist will measure the diameter of your calf muscles to see if one side is undergoing amyotrophy.

The final step of diagnosing muscle weakness focuses on ordering some imaging tests. Depending on the suspected diagnosis, your neurologist may order different tests.

If you recently had a stroke, an MRI is useful to determine the damaged areas of the cerebral cortex. It is also very helpful in assessing spinal cord injury.

Once all the data points to a single diagnosis, your doctor will confirm it.

The therapeutic complexity of weakness disorders correlates with the diversity of causes. Therefore, the entire treatment plan will be based on the underlying cause.

For instance, if the damage of a stroke is causing your muscle weakness, your neurologist may suggest physical rehabilitation to restore the lost tissue and functionality.

In some cases, the treatment is straightforward. For example, the discontinuation of a drug or the correction of an electrolyte imbalance should be enough to reverse your symptoms.