When a spinal cord is damaged by trauma, it also causes a concussion like injury to spinal cord which leads to total sensory and motor power loss and loss of all reflexes for initial some period which is followed by then gradual recovery of reflexes.
This state of sensory and motor loss along with total loss of reflexes following trauma is known as spinal shock.
Spinal shock begins within a few minutes of the injury, it make take several hours before the full effects occur. During spinal shock the nervous system is unable to transmit signals from brain to end organs as they are not routed by the spinal cord.
Usually the spinal shock recovers within 24 hours but may last over few weeks in less common cases. In some rare cases spinal cord shock can last for several more months.
Significance of Spinal Shock
There is a loss of signal transmission and the loss of these signals will result in loss of movements, sensations other body function. Complete loss of movement and sensation below the level of the spinal cord injury makes it difficult to assess the exact quantum of injury. Thus it is not possible to find the level, extent and severity of injury as patients would show compete neural loss.
The only way to find that is to wait for spinal shock to recover. Over the first few weeks the some of body systems adjust to the effects of the injury and their function improves. Therefore, during this time it is unlikely that an accurate prediction of any recovery or permanent paralysis can be made.
Pathophysiology of Spinal Shock
Exact cause of the spinal shock is not known. It is thought that acute injury causes depolarization of axons due to transfer of kinetic energy.
There are three phases of spinal shock
A complete loss or weakening of all reflexes below the level of spinal cord injury. This phase lasts for a day. The neurons involved in various reflex arcs the neural input from the brain due to spinal concussion become hyperpolarized and less responsive.
It occurs over the next two days, and is characterized by the return of some, but not all, reflexes. The first reflexes to reappear are polysynaptic in nature, such as the bulbocavernosus reflex.
Bulbocavernosus reflex can be checked by noting anal sphincter contraction in response to squeezing the glans penis or tugging on the Foley. It involves the S1, S2, S3 nerve roots and is spinal cord mediated reflex. Its presence signals the end of spinal shock.
Monosynaptic reflexes, such as the deep tendon reflexes, are not restored until Phase 3.
The reason reflexes return is the hypersensitivity of reflex muscles following denervation — more receptors for neurotransmitters are expressed and are therefore they are easier to stimulate.
Phases 3 and 4
These are characterized by hyperreflexia, or abnormally strong reflexes usually produced with minimal stimulation following sprouting of interneurons and lower motor neurons below the injury begin to attempt to reestablishment of synapses.
Identification of Spinal Shock
There is total paralysis, hypotonia & areflexia, and at its conclusion there may be hyperreflexia, hypertonicity, and clonus.
Return of reflex activity below level of injury (such as bulbocavernosus) indicates end of spinal shock.
Return of the of bulbocavernous reflex signifies the end of spinal shock, and if injury is complete, any further neurological improvement will be minimal. Complete absence of distal motor function or perirectal sensation, together with recovery of the bulbocavernosus reflex, indicates a complete cord injury, and in such cases it is highly unlikely that significant neurologic damage will return.
Spinal shock does not occur in the lesions that occur below the cord, and therefore, lower lumbar injuries should not cause spinal shock . If bulbocaveronsus reflex is absent in such cases may indicate a cauda equina injury
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