A tremor is an involuntary, rhythmic muscle movement, often appearing as shaking in the hands, arms, or other body parts. Shoulder impingement, by contrast, is a mechanical issue involving the shoulder joint’s soft tissues. Whether a localized musculoskeletal problem like shoulder impingement can cause a neurological symptom like a tremor requires investigating the mechanisms of both conditions. While direct causation is highly unlikely, understanding the anatomy of the shoulder and the origins of tremors reveals specific scenarios where the two symptoms might appear together, leading to a perceived link.
Understanding Shoulder Impingement
Shoulder impingement syndrome, also known as subacromial impingement, occurs when the tendons of the rotator cuff muscles become compressed and irritated. This compression happens as the tendons pass through the narrow subacromial space, which is the area beneath the acromion, the bony top of the shoulder blade. The tendons and the fluid-filled sac called the subacromial bursa can swell, causing them to rub against the bone during arm movement.
The symptoms of impingement are primarily localized and mechanical in nature. Individuals typically experience pain when lifting the arm, especially when moving it overhead or reaching behind the back. Other common symptoms include localized weakness in the shoulder muscles, limited range of motion, and a dull ache that may worsen at night, particularly when lying on the affected side. Impingement is fundamentally an issue of inflammation and mechanical friction within the joint capsule, not a disorder of the central or peripheral nervous system.
The Nature of Tremors
A tremor is a neurological symptom defined as a rhythmic, involuntary oscillation of a body part. It results from uncoordinated muscle contractions and is typically caused by a problem in the parts of the brain that control movement. Tremors are classified based on when they occur, such as a resting tremor, which happens when the muscles are relaxed, or an action tremor, which occurs during voluntary movement.
Action tremors include postural tremors, which appear when holding a position against gravity like extending the arms forward, and kinetic tremors, which manifest during movement toward a target. Essential tremor, the most common movement disorder, is a type of action tremor that often affects the hands and can be exacerbated by stress. Other causes are systemic or neurological, including medication side effects, alcohol withdrawal, an overactive thyroid, or conditions like Parkinson’s disease.
Examining the Potential Link Between Impingement and Tremors
Shoulder impingement syndrome, being a localized mechanical compression of tendons and bursae, does not directly cause the neurological dysfunction that leads to a tremor. The pathology of impingement involves soft tissue inflammation and friction, not the motor nerve pathways that originate in the brain and spinal cord. However, a perceived link often exists because both symptoms can be present simultaneously, usually due to a separate underlying cause or a secondary reaction.
Functional Tremors
One possible connection is the development of a functional tremor. Chronic pain from shoulder impingement can lead to high levels of stress and anxiety. This psychological state can trigger or enhance a functional tremor, which is an involuntary movement not caused by a primary neurological disease. In this scenario, the shoulder pain acts as a stressor, not a direct neurological cause.
Cervical Radiculopathy
The most likely scenario for a true neurological connection involves a condition known as cervical radiculopathy. The nerves that control the muscles of the shoulder, arm, and hand branch from the cervical spine (C5 to C8 nerve roots). Compression of a nerve root in the neck can cause pain that radiates into the shoulder, mimicking the pain of impingement, while simultaneously causing neurological symptoms further down the arm, such as weakness or tingling. Degenerative changes in the neck can compress a nerve root, leading to symptoms that feel like both a shoulder problem and a tremor, which are actually two manifestations of the same spinal issue.
When to Seek Medical Evaluation
If a person experiences both persistent shoulder pain and a new or worsening tremor, seeking medical evaluation is necessary to determine the correct source of the symptoms. For localized shoulder pain that is aggravated by movement, an orthopedic or physical therapy evaluation is typically the starting point, often involving X-rays or an MRI to assess the joint’s soft tissues and bone structure. This evaluation helps confirm or rule out the mechanical diagnosis of shoulder impingement.
A new or distinct tremor, especially one that occurs at rest or is unrelated to shoulder movement, warrants a neurological evaluation. A neurologist can perform a detailed examination to determine the tremor type and may investigate systemic causes like thyroid issues or medication side effects. Patients should mention both the shoulder pain and the tremor to their primary care physician so they can investigate the cervical spine as a potential common denominator. Imaging of the neck can reveal nerve root compression, which may be the true cause of both symptoms.