Subtle left arm pain may lead to chronic or more severe pain. Since pain is your body's way of telling you to pay attention, it is a good idea to find the source of pain and deal with it. Left arm pain can be from mechanical, structural, neurological and other causes.

Mechanical Causes

If your left arm pain worsens with movement or changes in posture, it may be mechanical, according to Dr. Nathan Wei, a board-certified rheumatologist. You could have left-side thoracic scoliosis--meaning your left shoulder is slightly higher than the right.

Muscle Strain

If you overuse neck, shoulder or arm muscles on the left side, pain is common, says Wei. If you have recently done repetitive arm motions such as painting or been involved in a new activity, muscle strain may cause subtle left arm pain. Such injuries can start out mild and intensify over time.

Neurological Causes

The brachial plexus is a group of nerves in the neck. If you have a pinched nerve, this can cause pain, tingling or numbness down one arm; nerve compression on the left side of the neck would affect the left arm. Cervical radiculopathy (neck pain) can travel down an arm, causing subtle to severe pain.

Chronic Conditions

Conditions such arthritis, degenerative disc disease (the breakdown of discs between vertebrae), or an autoimmune disease such as fibromyalgia might cause left arm pain. If left arm pain is a new symptom, ask your doctor whether your chronic condition may be causing it.

Other Considerations

Sometimes a simple fall or a bruise causes subtle pain. A past serious injury, such as a car accident, may be a source of recurring pain. Even a heart condition may cause pain in the left arm.

Source:

Arthritis Treatment and Relief: Neck and Scapular Pain

American Academy of Neurology: Neck and Back Pain

University of Maryland Medical Center: Cervical Radiculopathy

More Information:

Neurosurgery Today: Scoliosis

State University of New York Health Science Center: The Brachial Plexus

The Mayo Clinic: Chest Pain