Physiology, Deep Tendon Reflexes

The deep tendon reflex (DTR) examination is part of the neurologic exam. They were first described by Wilhelm Heinrich Erb and Carl Friedrich Otto Westphal more than a century ago. Their use continues to this day. The presence of hyporeflexia or hyperreflexia may indicate an underlying disease. Proper technique and interpretation of results are crucial to help in the diagnosis of many upper and lower motor neuron pathologic processes such as multiple sclerosis, amyotrophic lateral sclerosis, spinal cord injuries, spinal muscular atrophies, among others. They are sometimes referred to as muscle stretch reflexes.There are five primary deep tendon reflexes: bicep, brachioradialis, triceps, patellar, and ankle. Each reflex corresponds to a particular root and muscle and will evaluate the integrity of the root and associated nerve. Biceps: root C5-C6, biceps muscle Brachioradialis: root C6, brachioradialis muscle Tricep: roots C7, C8, triceps muscle Patellar: roots L2-L4, the quadriceps muscle Ankle(Achilles): S1-S2, gastrocnemius muscle To provide a standard scale for the evaluation of DTR, in 1993, the National Institute of Neurological Disorders and Stroke (NINDS) propose a grading scale from 0 to 4. It has been validated and is universally accepted. Sometimes, a plus sign (+) is added to distinguish it from the motor examination but does not represent a little more of the reflex elicited. Subjective clinical evaluation between different observers is more accurate in the lower extremity reflexes.NINDS grading of DTR ranges from 0 to 4. A normal response is grade 2 or 3. 0: Absent reflex, no reaction 1: Small reflex, less than normal, or obtained with reinforcement 2: Lower half of normal reflex 3: Upper half of normal reflex 4: Increased reflex. Clonus may be present, and it is always pathological