Introduction
An abdominal reflex is a reflex resulting from the contractions of the quadrants in the abdomen in response to stimulation. It is a superficial neurologic and polysynaptic reflex. It is elicited by tapping on the skin of the abdomen or the deeper bony structures around it. Abdominal reflex is an indispensable part of the neurologic examination. It can also help doctors decide the kind of investigation modes required further.
What Is the Abdominal Reflex?
An abdominal reflex is a reflex (involuntary sequence of actions in response to stimuli) resulting from the contractions of the quadrants in the abdomen in response to stimulation. It is a superficial neurologic and polysynaptic (several neurons are involved) reflex. It is elicited by tapping on the skin of the abdomen (superficial abdominal reflex) or the deeper bony structures around (deep abdominal reflex). The roots involved in this reflex are thoracic 8th to 12th. The local contraction of the abdominal muscles to sensory stimuli was to protect the internal viscera from damage.
How Can Abdominal Reflex Be Elicited?
Make the patient lie down comfortably on a bed in the supine position. Make sure their abdominal muscles are well relaxed. Then, using a blunt object, gently strike the abdominal skin toward the navel after dividing the abdomen into four quadrants. Observe the abdominal muscles as they contract in response to the stimuli. A normal response usually shows contraction of the abdominal muscles and the umbilicus moving toward the source of stimulation.
The deep abdominal reflexes can be observed by gently pressing the anterior abdominal wall with the fingers and tapping using a reflex hammer, eliciting an abdominal muscle contraction. However, abdominal reflex stretches are usually minimal in normal individuals.
It was proved that the clinically observed abdominal reflex was comparable to the late response to an electrically stimulated blink reflex by comparing the electromyographic response to an eclectic or scratch reflex.
Why Is an Abdominal Reflex Absent?
A reflex is noted as weak or absent. An absent reflex can be pathologic or physiologic. Physiologic reasons include anxiety, obesity, frailty (usually associated with aging), muscle laxity after multiple pregnancies, or abdominal surgery. As a result, they fatigue on repetitive testing and can be more asymmetric. The absence or weak abdominal reflex can denote a suprasegmental or upper motor neuron lesion; for example, after a stroke. Hence, it can be used to assess the level of injury in a neurology case.
Pathologic reasons can be:
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Multiple sclerosis (a condition where the insulating cover of the nerve cells in the brain and spinal cord is damaged).
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Neurogenic bladder (refers to the urinary bladder issues due to disease or injury of the nervous system that controls the urinary system).
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Brown-Sequard syndrome (caused by damage to one-half of the spinal cord resulting in paralysis and loss of proprioception on the same side of the injury and loss of pain and tactile sensation on the opposite side of the lesion).
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Chiari malformations (a structural defect in the cerebellum characterized by one or both tonsils of the cerebellum being displaced downward through the foramen magnum).
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Amyotrophic lateral sclerosis, also known as motor neuron disease or Lou Gehrig’s disease (is a neurodegenerative disease that causes the loss of motor neurons that control voluntary muscles).
What Are Abnormal Abdominal Reflexes?
Brisk abdominal reflexes are not clinically significant, though they are said to be brisk in congenital diplegia(cerebral palsy) and motor neuron disorders. It is absent in an upper motor neuron disorder and can be used to identify the anatomic location in the disorders of the thoracic spinal cord. Abdominal reflexes are less reliable than a sensory-level pin-prick and the presence of weakness in muscles.
It can suggest some pathologic abnormalities if present on one side and absent on the other. Pediatric surgeons use this to assess children with spinal scoliosis for a possible syrinx. They can come back after a stroke.
In patients with upper motor neuron disorders, deep abdominal reflexes are enhanced, in contrast to the superficial abdominal reflexes, which were diminished or absent. Like other cutaneous reflexes, the superficial abdominal reflexes are mediated across the midline through an intraspinal pathway.
About two-thirds of people with multiple sclerosis show an absence of abdominal reflexes. Hence, this is used in the early diagnosis of the condition. It also helps to differentiate between inflammatory and degenerative myelopathy, like motor neuron disease. However, the initial study did not consider the stage of the disease, and prospective studies still need to be done.
In some patients, changes in the dormancy of the responses from the abdominal muscles were encountered, which could not be explained by the clinical findings.
Examination of superficial abdominal reflexes in patients suspected of idiopathic scoliosis can help determine who would require magnetic resonance imaging(MRI) to rule out syringomyelia. Conversely, an absent superficial abdominal reflex in patients with scoliosis indicates underlying syringomyelia.
What Is the History Of Abnormal Abdominal Reflexes?
In 1876, Rosenbach first described the visible contractions of the abdominal muscles on gentle scratching of the skin. However, since these reflexes might be absent in patients having lesions in the central nervous system, some observers like Astwazaturow and Monrad-Krohn have postulated that the intrinsic reflex arc in normal people must traverse the highest levels of the nervous system.
Conclusion
Abdominal reflex is an indispensable part of the neurologic examination. It can also help doctors decide which further investigation modes might be required. For example, abdominal reflexes can be early in multiple sclerosis but late in motor neuron disorders. It can be seen that abdominal reflexes test the coherence of a broad swathe of the neurological system, like the neuromuscular junction, peripheral nerve, nerve root, spinal cord, and certain supraspinal centers. It is also very useful in the practical task of anatomic diagnosis. Abdominal reflexes can be used as ’go-to’ signs when the clinical diagnosis is complicated due to patient anxiety and becomes more helpful as the clinical experience develops. When taken along with the clinical presentation, they can be useful but extremely variable and misleading when considered alone.
