Some cause of muscle spasms are overuse or exercise of muscles on the left side, dehydration and atherosclerosis, according to MedicineNet. Nervous system disorders such as amyotrophic lateral sclerosis, multiple sclerosis and spinal cord injuries might be a cause of muscle spasms in various parts of the body. Hemifacial spasms are a specific type of spasm that occurs in the face and most often on the left side, notes the Dystonia Society.
Muscle spasms from overuse occur when there is a depletion of energy and fluid in the muscle cells, making them hyperexcitable, resulting in a contraction, states MedicineNet. In some cases, only part of the muscle spasms. This type of spasm is often seen in athletes, and when it occurs in conjunction with exposure to high temperatures, the condition is known as heat cramps. Atherosclerosis is a condition that occurs when the arteries narrow and cause a muscle spasm due to the decrease in nutrients in the blood supply.
Hemifacial spasm often develops in middle age and can interfere with vision, explains the Dystonia Society. The cause of the condition may be irritation of the facial nerve. There is no cure for this disorder, but botulinum toxin injections and surgery may be effective treatments.