Amyotrophic lateral sclerosis, better known as ALS or Lou Gehrig’s disease, is a degenerative condition that affects the motor neurons. The axons of motor neurons are found all over the body, specifically the muscles, but the respective cell body is located in the brain and spinal cord. They originate from the central nervous system and are projected to the muscles all around the body.
The first motor neuron starts in the motor cortex, the area of the brain responsible for movement. It connects with the second motor neuron in the spinal cord and this second neuron connects with different muscle fibers. ALS affects both the first and the second motor neurons that are involved in supplying the voluntary muscles with innervation. The degeneration and death of these neurons causes paralysis.
The disease usually appears in men and women between 50 to 70 years old. However, there are cases discovered in much younger patients, but according to research, it affects men up to 3 times more than women. There is a rare form of ALS that is inherited, which is responsible for only 10% of cases. The rest of the ALS cases are considered to be sporadic.
The exact cause is still unknown. There are multiple theories that try to explain the origin of the disease. The most supported hypotheses point to a possible combination between alterations of the immune system and the action of environmental factors. Several studies have shown the relationship between the use of certain agricultural pesticides and the occurrence of ALS, other studies have also revealed a possible association between the disease and certain fungal infections.
On the genetics side, several mutations related to this condition have been identified, in the forms of inherited amyotrophic lateral sclerosis; it has been proven that the most frequent alteration is a mutation in the superoxide dismutase 1 (SOD1) gene. In random cases, polymorphisms have been found to possibly be related to the development of this illness.
The symptoms of ALS are the result of the destruction of motor neurons. It usually begins with weakness in the distal part of the limbs in an asymmetric way, meaning, they do not affect both hands and feet at the same time. Patients can also stumble, drop objects and some have difficulty speaking. Weakness slowly gives way to paralysis, ALS is progressive. Paralysis affects the different voluntary muscles and in a disordered manner, the only muscles that are not affected until the very advanced stages are the extrinsic muscles of the eye and the sphincters. Therefore, despite suffering from paralysis, these patients are able to move their eyes and control urination and defecation.
The paralysis developed in ALS is a ‘rigid’ type of paralysis where stiffness takes over and they cannot move. Babinski’s sign is also present. By lightly stroking the sole of the feet (as if tickling), the big toe stretches up while the rest of the fingers are fanned out. This is Babinski’s sign and is indicative of injury of the first motor neuron, so its presence is always pathological. When we tickle the feet of a healthy person, the toes point downwards, not upwards. The appearance of this sign is normal exclusively in neonates, as it should disappear during infancy and never return. Hence, an adult should never show an extended toe after stimulation, otherwise, it is indicative of a neurological disorder.
The critical point of ALS comes when paralysis affects the pectoral muscles because it compromises the respiratory function of the patient. From this moment on, the installation of respiratory supports is essential.
It has been recently discovered that in addition to motor symptoms, non-motor neurological symptoms appear. Impairment of superior functions such as loss, concentration, memory and signs of dementia, among others.
Paralysis also affects the cranial nerves, which are the ones that innervate the head and neck structures. Therefore, it brings about difficulty or inability to swallow (dysphagia), presenting a risk of choking, aspiration and difficulty or inability to articulate words (dysarthria).
ALS patients can present a neurological state called ‘lability’, which is when they lack control of emotional responses, specifically, erratic laughing and weeping. These alterations are included in the so-called ‘pseudobulbar syndrome’ which is due to a lesion of the rachidian bulb.
The diagnosis of this illness is difficult since there is no standard test that allows the obtaining of a definitive answer. Diagnosis should be based on medical criteria and the result of multiple complementary tests such as magnetic resonance, electromyography (measures the electrical activity of the muscles), tests of nerve conduction velocity and analysis of the cerebrospinal fluids. Its diagnosis usually causes a serious emotional impact, both in patients and their family. Depression at the time of diagnosis is frequent as well as during the course of the disease.
The prognosis of ALS is fatal. The estimated life expectancy is about 3 years as a maximum, there is no curative treatment. Currently, the only drug available is Riluzole which only increases the life expectancy by a few months. Nowadays, the only possible treatment is aimed at improving the quality of life of these patients. Due to the high degree of disability that they suffer, palliative and psychological support is required. As for family members, the high degree of dependency of ALS patients can bring about the the appearance of ‘caregiver burnout’, so it’s also recommended for them to have psychological support from professionals, friends and other members of the family.