Locked-in syndrome is a rare neurological disorder in which there is complete paralysis of all voluntary muscles except for the ones that control the movements of the eyes. Individuals with locked-in syndrome are conscious and awake, but have no ability to produce movements (outside of eye movement) or to speak (aphonia). Cognitive function is usually unaffected. Communication is possible through eye movements or blinking. Locked-in syndrome is caused by damaged to the pons, a part of the brainstem that contains nerve fibers that relay information to other areas of the brain. Individuals with locked-in syndrome classically cannot consciously or voluntarily chew, swallow, breathe, speak, or produce any movements other than those involving the eyes or eyelids. Some affected individuals can move their eyes up and down (vertically), but not side-to-side (horizontally). Affected individuals are bedridden and completely reliant on caregivers. Despite physical paralysis, cognitive function is unaffected. Individuals with locked-in syndrome are fully alert and aware of their environment. They can hear, see and have preserved sleep-wake cycles. Affected individuals can communicate through purposeful movements of their eyes or blinking or both. They can comprehend people talking or reading to them. Individuals with locked-in syndrome often initially are comatose before gradually regaining consciousness, but remain paralyzed and unable to speak. The locked-in syndrome may be classified in three different clinical forms, according to the traditional classification of Bauer. This classification is based on the amount of motor outputs, which are preserved in the patients.
It talks about a pure form when the patient loses the control of all body movements with the exception of blinking and vertical eye movements; an incomplete form when some voluntary movements other than eye movements are preserved and a total form when a complete loss of motor function occurs. The last condition is particularly dramatic as the patients are completely unable to interact with the environment and to express their needs and thoughts. Although the locked-in syndrome appears as the most dramatic form of motor disability one can imagine, some scientific reports indicate that the quality of life of patients is not so poor as expected. A recent survey investigated the self-reported quality of life of chronic patients with locked-in syndrome and concluded that many patients have a happy and meaningful life, especially when proper social services help patients to have a normal role at home as well as in the community. Patients with locked-in syndrome are traditionally considered cognitively intact as all the cerebral structures with the exception of the ventral portion of the pons of the brain are apparently preserved. However, recent evidence suggests that the patients can develop some non-motor symptoms including motor imagery defects, pathological laughter and crying, and difficulties in the recognition of some facial expressions.
The interruption of the cortico-ponto-cerebellar pathways, by means of the the same lesion causing the locked-in syndrome, may be responsible for the appearance of these clinical manifestations. However, these symptoms are not detected in all affected individuals and are currently under further investigation. The recognition of motor imagery defects deserves special attention because these symptoms, whenever present, may interfere with the success of rehabilitation strategies. Locked-in syndrome is most often caused by damage to a specific part of the brainstem known as the pons. The pons contains important neuronal pathways between the cerebrum, spinal cord and cerebellum. In locked-in syndrome there is an interruption of all the motor fibers running from grey matter in the brain via the spinal cord to the body’s muscles and also damage to the centers in the brainstem important for facial control and speaking. Damage to the pons most often results from tissue loss due to lack of blood flow (infarct) or bleeding (hemorrhage) – less frequently it can be caused by trauma. An infarct can be caused by several different conditions such as a blood clot (thrombosis) or stroke. Additional conditions that can cause locked-in syndrome include infection in certain portions of the brain, tumors, loss of the protective insulation (myelin) that surrounds nerve cells (myelinolysis), inflammation of the nerves (polymyositis), and certain disorders such as amyotrophic lateral sclerosis (ALS).