Is unilateral weakness (weakness on one side of the body) of the left upper and lower extremities compared to the right side, in a right-handed (right hand dominant) individual, considered normal in an otherwise healthy adult?

From the Guidelines

Unilateral weakness on one side of the body, particularly when it affects both the upper and lower extremities, is not considered normal in an otherwise healthy adult, regardless of handedness, and warrants prompt medical evaluation. While it's common to have slightly more strength and dexterity in the dominant side, a significant difference in strength between the left and right sides of the body could indicate a neurological issue such as a stroke, multiple sclerosis, or other conditions affecting the brain or nervous system 1. This type of asymmetrical weakness, especially if it affects both the arm and leg on the same side, is particularly concerning because it suggests a problem in the opposite hemisphere of the brain or along the nerve pathways.

The provided evidence from the American Heart Association 1 and JAMA Pediatrics 1 supports the importance of early diagnosis and intervention in neurological conditions. For instance, the use of assessments like the Fugl-Meyer Motor Assessment–UE subscale 1 can help identify unilateral weakness and guide rehabilitation efforts. However, the key takeaway is that any significant unilateral weakness should be evaluated promptly by a healthcare provider, especially if it developed suddenly, as this could represent a medical emergency requiring immediate treatment.

Some key points to consider include:

• The pattern of weakness on one side of the body (hemiparesis) is a red flag for neurological conditions 1.
• Early intervention for conditions like stroke can significantly improve outcomes 1.
• A thorough medical evaluation, including a detailed history and physical examination, is necessary to determine the underlying cause of unilateral weakness.
• The use of standardized assessments, such as those listed in the American Heart Association guidelines 1, can help guide diagnosis and treatment.

In summary, unilateral weakness on one side of the body is a concerning symptom that requires prompt medical attention, and individuals experiencing this symptom should not wait to see if it improves on its own, as early intervention can significantly improve outcomes 1.

From the Research

Unilateral Weakness in Healthy Adults

• Unilateral weakness, or weakness on one side of the body, is not typically considered a normal finding in an otherwise healthy adult 2, 3, 4, 5.
• Electrodiagnostic studies, such as nerve conduction studies (NCS) and electromyography (EMG), can be used to evaluate the peripheral nervous system and identify potential causes of unilateral weakness 2, 3, 4, 5.
• These studies can help determine if the weakness is due to a problem with the nerve, muscle, or neuromuscular junction, and can also help identify the location and extent of any damage 2, 3, 4, 5.

Normal Variations in Strength

• While some variation in strength between the two sides of the body is normal, significant unilateral weakness is not typically considered a normal finding 2, 3, 4, 5.
• Clinical practice guidelines emphasize the importance of evidence-based medicine in evaluating and managing patients with neurological symptoms, including unilateral weakness 6.
• However, the provided studies do not specifically address the question of whether unilateral weakness on the left side in a right-handed individual is considered normal in an otherwise healthy adult.

Diagnostic Evaluation

• A thorough diagnostic evaluation, including electrodiagnostic studies and clinical examination, is necessary to determine the cause of unilateral weakness in an individual 2, 3, 4, 5.
• The results of these studies can help guide further evaluation and treatment, and can also help identify potential underlying conditions that may be contributing to the weakness 2, 3, 4, 5.