The deep tendon reflexes are a vital component of the neurological examination. The test is performed by tapping a reflex hammer over a tendon. When the tendon is tapped, it stretches, sending a signal through the nerves, to the spine. The spine then sends a signal back to the muscles, causing the muscle to contract. This is known as the reflex arc. For a deep tendon reflex to be normal, you must have proper functioning of the tendon, muscle and nerve. (See References 1) The response of the muscle is graded as hyperactive, normoactive, or hypoactive. Deep tendon reflexes are determined to be hypoactive, when they do not respond to tapping of the tendon.
Peripheral Neuropathy
Peripheral neuropathy primarily manifests as a burning discomfort in the feet or hands, with hypoactive reflexes found on physical examination.The reflexes most often affected are the ankle-jerks. It is a frequent complication of a number of medical conditions. This includes diabetes, alcoholism, autoimmune diseases, as well as heavy metal toxicity. Nearly half of those diagnosed with diabetes, will develop peripheral neuropathy. (See References 2)
Herniated Discs
Herniated discs in the spine, may also cause hypoactive reflexes. When a disc herniates, the inner jelly solution leaks out. Since the outer core is directly next to the spinal nerve roots, the herniation will place pressure on the nerve. The compression of the nerve produces pain into the arms or legs, depending on the site of the herniation. Discs herniated in the cervical area will cause pain into the arms. Lumbar herniated discs are associated with leg pain, referred to as sciatica. (See References 3) Due to disruption of the nerve pathway, the deep tendon reflex will be absent of diminished.
Myasthenia Gravis
Myasthenia gravis is a condition which interferes with the communication between nerves and muscle. When a nerve is stimulated, it releases a hormone named acetylcholine. Acetylcholine in turn tells your muscle to contract. Myasthenia gravis results when your body produces a chemical which breaks down acetylcholine, therefore the normal interaction between muscle and nerve is lost. This results in symptoms of extreme fatigue and weakness. (See References 4)The muscle will be unable to contract and the reflexes will be diminished.
Rare Etiologies
Hypoactive deep tendon reflexes in some instances are caused by rare genetic or acquired disorders. These include Charcot-Marie-Tooth disease, Guillain-Barre syndrome, or CIDP. These conditions are exceedingly rare. Symptoms include severe progressive weakness and muscle wasting. (See References 5) They are diagnosed with the use of an electromyography study, perfomed by your physician.
References
- Neuroexam: Deep Tendon Reflexes
- MayoClinic: Peripheral Neuropathy
- Spine-Health: Lumbar Herniated Disc
- MayoClinic: Myasthenia Gravis
- "Current Medical Diagnosis & Treatment"; Acne Vulgaris; Stephen J. McPhee, MD, Maxine A. Papadakis, M.D.; 2007
