15 Arm and Leg Asymmetries That Prompt Neurological Evaluation

6. Reflex Asymmetries - Upper and Lower Motor Neuron Differentiation

Asymmetrical deep tendon reflexes between corresponding limbs serve as fundamental indicators of nervous system pathology and provide crucial information for differentiating between upper motor neuron, lower motor neuron, and mixed neurological conditions. Hyperreflexia on one side compared to the other typically suggests upper motor neuron pathology affecting the corticospinal tract, with conditions such as stroke, spinal cord compression, or multiple sclerosis commonly causing these asymmetrical presentations. The presence of pathological reflexes such as the Babinski sign, Hoffman's reflex, or sustained clonus on the hyperreflexic side further supports upper motor neuron involvement and may indicate the need for urgent neuroimaging to identify potentially treatable causes such as spinal cord compression or brain lesions. Conversely, asymmetrically diminished or absent reflexes suggest lower motor neuron pathology, peripheral neuropathy, or radiculopathy affecting the reflex arc components including sensory nerves, spinal cord segments, motor neurons, or peripheral motor nerves. Radiculopathy often presents with specific patterns of reflex loss corresponding to the affected nerve root levels—for example, C5-C6 radiculopathy may cause diminished biceps and brachioradialis reflexes, while L4 radiculopathy may affect the patellar reflex. The evaluation of reflex asymmetries requires systematic testing of all major deep tendon reflexes using consistent technique and grading scales, with attention to both the presence and quality of the reflex response. Electromyography and nerve conduction studies can help differentiate between various causes of reflex abnormalities, while magnetic resonance imaging of the brain or spine may be necessary to identify structural causes of upper motor neuron signs that require specific interventions.