Muscle stretch reflexes

The muscle stretch reflex, also called the myotatic reflex, is a reflex arc that causes a muscle to contract in response to a change in length. This reflex helps maintain muscle tone and support posture.

To elicit a muscle stretch reflex, the selected tendon is usually struck directly and precisely with a reflex hammer. An exception is the biceps reflex, which is best tested by tapping the tendon with the thumb placed over it. The limb being tested should be relaxed and in a flexed or semi-flexed position.

The Jendrassik maneuver can be used during the test to enhance a muscle reflex that is difficult to elicit:

• To test the reflexes of the upper extremities, the patient is asked to cross their ankles and then isometrically attempt to abduct their legs.
• To test the reflexes of the lower extremities, the patient is asked to interlock their fingers and then isometrically attempt to pull their elbows apart.

Jendrassik maneuver, which is used during the test to reinforce a muscle reflex.

Muscle stretch reflex scales

Two muscle stretch reflex scales can be used to classify a reflex:

1. National Institute for Neurological Disorders
2. Stroke Scale (NINDS) and the Mayo Clinic scale.

NINDS Scale

The NINDS scale uses the following five-level rating system:

1. Absent (areflexia). The absence of a reflex means an interruption of the reflex arc. 1, slight and less than normal (hyporeflexia).
2. in the lower half of the normal range.
3. in the upper half of the normal range (rapidly).
4. intensified and more than normal (hyperreflexive).

One of the problems with the NINDS scale is that there is no separate category for "normal", so one has to choose between a "low normal" and a "high normal".

Mayo Clinic Scale

The Mayo Clinic uses the following nine-point scale:

1. Absent: -4
2. Only triggerable: -3
3. Low: -2
4. Moderately low: -1
5. Normal: 0
6. Great: +1
7. Very lively: +2
8. Exhaustible clone: ​​+3
9. Continuous Clonus: +4

A missing or exaggerated reflex is only significant if it is associated with one of the following factors:

1. The reflex is unusually brisk compared to reflexes from a higher spinal level.
2. The exaggerated reflexes are related to other findings of UMN disease.
3. The lack of reflexes is related to other findings of LMN disease.
4. The reflex amplitude is asymmetrical. Reflex asymmetry has greater pathological significance than the absolute activity of the reflex—a bilateral patellar reflex of 3 is less significant than a 3 on the left and a 2 on the right. Furthermore, in cases where the reflex findings are symmetrical but either increased or decreased, further investigation is required. For example, a patient may present with symmetrically brisk patellar and Achilles tendon extender reflexes, while simultaneously… Absent stretch reflexes in the upper extremity require further investigation (this is a typical finding in amyotrophic lateral sclerosis or Lou Gehrig's disease, a mixed UMN and LMN pathology).

The physiology of a myotatic reflex.

Results of the muscle reflex test

The findings of muscle reflex testing can appear as a generalized or local phenomenon:

1. Generalized hyporeflexia. The causes of generalized hyporeflexia range from neurological diseases, chromosomal metabolic disorders and hypothyroidism to schizophrenia and anxiety disorders.
2. Non-generalized hyporeflexia. In general, an asymmetrically diminished or absent reflex indicates a pathology directly affecting the reflex arc, such as a left limb nerve (LMN) lesion or sensory paresis, which may be segmental (root), multisegmental (cauda equina), or non-segmental (peripheral nerve). Non-generalized hyporeflexia can result from peripheral neuropathy, spinal nerve root compression, and cauda equina syndrome. Therefore, it is important to test more than one reflex and evaluate the information obtained from the examination before drawing conclusions about the relevance of the findings.

In situations where an increased or brisk reflex is observed, the normal function of the central nervous system (CNS) in integrating reflexes may be disrupted, suggesting a lesion of the unilateral neuron (UMN), such as brainstem or brain damage, spinal cord compression, or a neurological disorder. However, a distinction must be made between a brisk and a hyperreflexive reflex.

True neurological hyperreflexia contains a clonic component and suggests involvement of the central nervous system (UMN). The clinician should also note any additional recruitment that occurs during the target's reflex contraction. A brisk reflex is a normal finding unless it masks hyperreflexia caused by improper testing technique. Unlike hyperreflexia, a brisk reflex does not have a clonic component.

As with hyporeflexia, the physician should assess more than one reflex before concluding that hyperreflexia is present. The presence of UMN impairment can be confirmed by the presence of pathological reflexes (see next section).

References and more

1. Currier RD, Fitzgerald FT: Nervous system. In: Judge RD, Zuidema GD, Fitzgerald FT, eds. Clinical Diagnosis, 4th edition. Boston, MA: Little, Brown and Company, 1982: 405–445.
2. Manschot S, van Passel L, Buskens E, Algra A, van Gijn J. Mayo and NINDS scales for assessing tendon reflexes: between observer agreement and implications for communication. J Neurol Neurochirurgische Psychiatrie. 1998 Feb;64(2):253-5. doi: 10.1136/jnnp.64.2.253. PMID: 9489542; PMCID: PMC2169960 .
3. Soloman J, Nadler SF, Press J: Physical examination of the lumbar spine. In: Malanga GA, Nadler SF, eds. Physical examination of the musculoskeletal system – an evidence-based approach. Philadelphia, PA: Elsevier-Mosby, 2006: 189–226.
4. Halle JS: The neuromusculoskeletal scan examination. In: Voight ML, Hoogenboom BJ, Prentice WE, eds. Musculoskeletal Interventions: Techniques for Therapeutic Exercises. New York, NY: McGraw-Hill, 2007:47–80.
5. Adams RD, Victor M: Principles of Neurology, 5th edition. New York, NY: McGraw-Hill, Department of Health Professions, 1993