Spinal Shock Definition and Significance

Spinal shock is a state of total sensory, motor power loss and loss of all reflexes for a  period which is followed by the gradual recovery of reflexes. Spinal shock can occur in case of spinal cord injury.

Spinal shock begins within a few minutes of the injury, it may take several hours before the full effects occur. During spinal shock, the nervous system is unable to transmit signals from the 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 a few weeks in less common cases. In some rare cases, spinal cord shock can last for several more months.

Pathophysiology of Spinal Shock

The exact cause of the spinal shock is not known. It is thought that acute injury causes depolarization of axons due to the transfer of kinetic energy.

There are three phases of spinal shock

Phase 1

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.

Phase 2

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 the 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 the 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 the level of injury (such as bulbocavernosus) indicates an end of the spinal shock.

Return of the of bulbocavernosus reflex signifies the end of the spinal shock, and if the injury is complete, any further neurological improvement will be minimal. The 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  bulbocavernosus reflex is absent in such cases may indicate  a cauda equina injury

The 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 the injury as patients would show a complete neural loss.

The only way to find that is to wait for the spinal shock to recover. Over the first few weeks, the somebody 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.