Definition/Introduction
The grasp reflex, also known as the palmar reflex, is a primitive, prehensile, involuntary response to a mechanical stimulus present in a newborn. As the name implies, the action resembles a grasping motion of the hand. This reflex appears around 16 weeks of gestation and can be elicited in preterm infants as young as 25 weeks of postconceptional age (see Image. Palmar Reflex).[1][2][3][4] To elicit the reflex, the infant is laid in a symmetrical supine and comfortable position while he or she is awake.[5] The examiner strokes the palm of the infant with his or her index finger.[4][6] The response to this stimulus comprises 2 phases: finger closure and clinging.[4] The infant's fingers undergo flexion to enclose the examiner's finger (finger closure). The pressure applied to the palm produces traction on the fingers' tendons, leading to the clinging action.[7][4][7] The thumb is not affected by this reflex.
The higher brain centers regulate the grasp reflex, though it is a spinal reflex. The afferent nerve fibers include the ulnar and median sensory nerves that supply the palmar surface. The spinal relay center is in the cervical spinal cord, and the efferent nerve fibers have the motor nerves that supply the hand's flexors and adductors.[8][9] The brain's premotor cortex, supplementary cortex, and cingulate motor cortex are implicated in controlling the grasp reflex through the spinal interneurons.[10][11][12]
A similar reflex is observed in the foot called the plantar grasp reflex. This reflex is observable by stimulating the medial plantar surface of the foot. When the foot grasp reflex is positive, upon such stimulation, the lateral surface of the foot will react to create an indentation in the plantar surface, resembling a cup (see Image. Plantar Reflex).[6] The grasp reflex is considered a primitive reflex, similar to the suck, snout, and palmomental reflexes.[6][13] Primitive reflexes are generally present at birth but disappear upon maturation of the nervous system as a part of normal development.[13][14]
Issues of Concern
The grasp reflex typically disappears by 6 months of age, signifying cortical maturation and the development of voluntary motor milestones.[8][15] However, a weak reflex before 6 months or persistence of the reflex even after 6 months implies an underlying is associated with focal lesions in the central nervous system (CNS) or diffuse neurodegeneration, as observed in a broad range of neurodegenerative diseases.[13] As such, the reemergence of the grasp reflex causes concern for a neuropathological process. Further, the presence of an unwanted grasp reflex may be a disabling feature of neurodegenerative diseases, contributing to decreased quality of life.[13]
A weak response presents in peripheral nerve involvement, such as an injury to the roots, plexus, or spinal cord.[16] Persistence of the reflex beyond 6 months is usually present in spastic cerebral palsy.[17] The grasp reflex can also reappear in adulthood, indicating a cortical lesion affecting the medial or lateral frontal cortex (eg, ischemic or hemorrhagic stroke).[10][11][18] Injury to the higher center removes the cortical inhibition, leading to the release of the primitive reflex.[10] Typically, the grasp reflex has been observed already in the fetal period when the baby grasps the umbilical cord. In premature babies, the palmar reflex follows the same time frame as babies born at term.
Clinical Significance
The grasp reflex's original purpose is vestigial or unknown, though it can aid in diagnosing specific pathologies. This serves nothing more than a rudimentary phylogenetic function necessary for the arboreal life of newborn monkeys.[12] Babies a few months old are unable to organize movements to grab an object voluntarily. The palmar reflex probably creates a basic motor pattern that lays the foundation for obtaining this voluntary ability. Furthermore, this reflection creates interaction and bonds between the infant and the adult.
The precise neural circuit mapping of the grasp reflex has not been characterized. Research has shown that ulnar and median nerve stimulation at the wrist will yield a grasp reflex response in 40 milliseconds, suggesting that the reflex gets mediated at the spinal cord level.[9][12] Inhibition of this reflex arc ultimately comes from higher cortical brain centers in conjunction with brainstem input and becomes active as the cortex matures.[13][8] Various studies have attempted to map precisely where this inhibition comes from but have yielded inconsistent results.[13] Proposed regions involved include the cerebellar hemispheres, supplementary motor area [11], anterior cingulate gyrus, frontal lobe areas, and parietal lobe.[10][11][4][18]
Clinical Application
From a clinical point of view, the reflex can be abnormal if the child responds with an exaggerated reflex (within 6 months of life) or is weak; equally, this reflex is a clinical neurological hallmark if it persists. The grasp reflex may be absent, and this event highlights a peripheral neurological injury or spinal cord involvement, particularly with an asymmetric response. Several conditions are associated with the reemergence of the grasp reflex in later life, including Parkinson disease, progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies frontotemporal dementia, and normal pressure hydrocephalus.[13][19] As such, eliciting a grasp reflex in an adult patient suggests an underlying neurological disease but is not a highly specific finding. The reemergence of the grasp reflex in later life is also reportedly reversible in patients with temporarily diminished cortical activity, such as drowsy or semi-comatose patients.[13][4] The shared theme across these various conditions is the impairment of higher-level nervous system function, eliminating the inhibition to brainstem areas mediating the grasp reflex. Without appropriate inhibition, the grasp reflex can reemerge in later life.
Although the grasp reflex may be present in various neurological disorders, its presence is not always pathologic. Like all primitive reflexes, the grasp reflex is normally present in infancy. The grasp reflex has been reportedly observed as early as 16 weeks gestation and is generally observable by the third trimester.[1][20] The reflex persists until between 4 and 6 months postpartum.[4]
After infancy, the grasp reflex is rarely observable without relation to an underlying pathology. The prevalence in healthy adults aged 65 and older is estimated to be 0.1%. The prevalence in adults 65 and older with mild cognitive impairment is estimated to be 1.7%, and the prevalence in adults 65 and older with dementia is estimated to be 18.4%.[14] Thus, although observation of the grasp reflex in healthy adults is possible, its presence is correlated with cognitive decline or some neurological pathology.[14][21]
If a brain lesion is central, the reflex could last longer, eg, in the presence of spastic hemiplegia or quadriplegia; on the contrary, if the lesion is typical of an infantile cerebral palsy or athetoid type, the palmar grip is weak. Spinal interneurons are essential in modulating the periphery and upper nonmotor centers during growth. As the brain matures, the higher motor centers will better control the spinal circuits, and a voluntary hand-held grip is present. In the event of injury, the upper nonmotor centers could play a role in this reflex's appearance in children and adults.
According to recent animal studies, another reason for the palmar reflex's alteration is an inadequate (minor) amount of melatonin from the female towards the fetus. This absence or decreased availability will alter the upper centers' functions, with an abnormal palmar reflex. Maternal melatonin provides the fetus with valuable information for internal rhythms (photoperiodic information) and future nervous patterns for extrauterine development. According to an observational study on children, the grasp reflex is stronger if the baby is hungry and could indicate the baby's need to be breastfed.
Treatment of Adult Grasp Reflex
A paucity of scholarship specifically addresses the treatment of the grasp reflex in adults. Instead, research has primarily focused on treating the overlying neurological disorders likely responsible for its reemergence. However, the presence of the grasp reflex can contribute to disability in patients with neurodegenerative conditions and hinder their ability to complete activities of daily living.[13] As such, interventions targeted at eliminating the grasp reflex could be useful.
A case study of 3 patients who had alcohol dependence and were already receiving treatment with benzodiazepines reported some success in eliminating the grasp reflex by treating with acamprosate.[22] The study noted that primitive reflexes, including the snout and grasp reflex, were eliminated within 24 hours of starting acamprosate.[22] Although this study showed promising results, we do not have data about the long-term outcomes of these patients regarding the reemergence of their primitive reflexes. Further, the sample size of 3 patients with a single disease process limits the generalizability of these study results. Nevertheless, this study's data suggest a potential pharmacological treatment for the grasp reflex and provide a starting point for future follow-up work.
Other suggested treatments involve injecting botulinum toxin into the muscles involved in the grasp reflex.[13] By preventing acetylcholine release from the presynaptic neurons at the neuromuscular junction, botulinum toxin could produce flaccid paralysis in the affected muscles that may be beneficial in cases of an unwanted grasp reflex. Although an interesting idea, this strategy has yet to be tested explicitly in the setting of relieving a grasp reflex.
Another suggested therapy is orthotics, eg, splints.[13] A carefully designed splint could oppose unwanted flexion during the grasp reflex. This therapy has not been subject to rigorous study, which allows for follow-up investigations.
Nursing, Allied Health, and Interprofessional Team Interventions
The grasp reflex, a crucial neurological assessment in neonates, requires an interprofessional approach for optimal patient care. Physicians, particularly pediatricians, and neurologists, are responsible for diagnosing conditions like cerebral palsy or peripheral nerve injuries, often identified by abnormal grasp reflexes. Early diagnosis is paramount, as delays impact prognosis. Obstetricians play a crucial role in preventing peripheral nerve injuries by managing high-risk pregnancies and intervening in cases of shoulder dystocia.
Nurses provide essential bedside care, including early stimulation and support for bedridden patients. Pharmacists may assist in managing medications related to treatment plans. Advanced practitioners contribute to diagnosis and treatment plans, often collaborating closely with physicians. Occupational and physical therapists are integral in developing and implementing therapy plans to address the grasp reflex, improving motor function and independence. Interprofessional communication is critical, with regular team meetings, shared treatment plans, and open discussions among all clinicians to ensure coordinated care. This collaborative approach, encompassing early intervention, appropriate therapies, and ongoing support from the healthcare team and families, is essential for optimizing patient outcomes and improving the quality of life for individuals affected by conditions associated with abnormal grasp reflexes.
Nursing, Allied Health, and Interprofessional Team Monitoring
Any abnormality in the palmar grasp reflex warrants monitoring the underlying disease rather than the reflex itself. The child's growth and development should be assessed at every visit, as a complete physical examination gives a better prognosis than a single entity. This includes features like the muscles' tone, the bulk of the muscles, respiration, and the cry. Consistent monitoring, motivation, and intervention are essential for better outcomes.
Testing for the grasp reflex is relatively simple, involving stimulating the hand's palmar surface in a distal direction. All members of the healthcare team can be trained to perform this test. As such, various healthcare team members can monitor patients for the grasp reflex. The new onset of a grasp reflex or a strengthened response of a preexisting grasp reflex may indicate the progression of underlying pathology. Members of the healthcare team should be cognizant of this finding’s significance.
