Noticing an involuntary shaking in the same arm as a painful shoulder can be confusing, leading many to question if a mechanical injury can trigger a neurological symptom. Shoulder impingement involves inflammation and compression of soft tissues, a localized physical problem, while a tremor is a rhythmic, involuntary muscle movement typically originating in the nervous system. This article investigates whether a direct, medically recognized link exists between the physical trauma of an impinged shoulder and the appearance of a systemic tremor. Understanding the distinct nature of each condition is the first step toward determining the cause of the shaking.
Understanding Shoulder Impingement
Shoulder impingement syndrome, also known as subacromial impingement, occurs when the soft tissues in the shoulder become compressed as they pass through the narrow space beneath the acromion. This subacromial space houses the rotator cuff tendons, particularly the supraspinatus tendon, and the bursa. Repetitive overhead arm movements are a common cause, leading to irritation and swelling of these tissues.
When the tendons or the bursa swell, the space available for movement decreases, causing them to be pinched against the acromion during certain arm motions. This mechanical compression results in the primary symptoms: pain, which is often worsened by lifting the arm overhead or reaching behind the back, and localized muscle weakness. The pain is typically described as a dull ache that may interfere with sleep, especially when lying on the affected side.
Primary Causes of Involuntary Tremors
Involuntary tremors are generally classified by their appearance and origin, which is almost always neurological or related to systemic metabolism. The most common movement disorder is Essential Tremor, characterized by a bilateral action tremor that occurs when a person is actively using their hands or maintaining a posture, such as holding a cup. This tremor is progressive and typically affects both sides of the body, often involving the head or voice.
Another major category is the Parkinsonian Tremor, which is distinct because it is primarily a resting tremor, meaning the shaking is most noticeable when the limb is completely relaxed. This type of tremor is often asymmetrical and may be accompanied by other neurological signs like rigidity or slow movement. A third common type is Enhanced Physiologic Tremor, which is an amplified version of the slight, normal tremor everyone experiences.
This physiologic tremor is not caused by a neurological disease but is often triggered or worsened by external factors. These exacerbating factors include high stress or anxiety, excessive consumption of caffeine, fatigue, or underlying metabolic issues like an overactive thyroid or low blood sugar. Enhanced Physiologic Tremor is potentially reversible once the underlying cause is addressed.
Examining the Potential Connection Between Impingement and Shaking
A direct, causal link between mechanical shoulder impingement and a chronic neurological tremor is not recognized in medical literature. Impingement is a localized, inflammatory condition, while true tremors are rooted in abnormal nerve signaling within the brain. However, the two conditions can appear related due to indirect mechanisms.
One possible indirect link is severe pain leading to muscle guarding or localized instability, which can be mistaken for a tremor. When the shoulder joint is severely painful, the surrounding muscles tense up involuntarily to protect the area. This sustained tension can result in localized, rapid muscle twitching or instability in the arm, which is a muscular, pseudo-tremor.
A second connection involves the medications used to manage the shoulder pain. Patients with significant shoulder pain, including impingement, are sometimes prescribed muscle relaxants to alleviate muscle spasms. Certain muscle relaxants, such as Orphenadrine, list tremor as a potential side effect. If the shaking began shortly after starting a new medication, a drug-induced tremor may be the actual cause.
The shoulder impingement and the tremor may also be two separate conditions occurring simultaneously, which is a simple coincidence. Essential Tremor is a common disorder, and having it alongside a common orthopedic issue like shoulder impingement is not mutually exclusive. Treating the shoulder will resolve the pain but will not affect the underlying neurological tremor, confirming they are independent issues.
When Tremors Require Medical Evaluation
While the shaking may be harmless, certain characteristics of a tremor warrant a prompt medical evaluation to rule out a serious neurological disorder. A physician should be consulted if the tremor occurs when the arm is completely at rest, as this is a hallmark feature of Parkinsonian Tremor. Tremors that appear suddenly and progress rapidly are also considered a red flag.
Other concerning signs include a tremor that is strictly unilateral, affecting only one side of the body, or one accompanied by neurological symptoms. These symptoms include changes in balance or gait, muscle rigidity, or difficulties with speech. If a tremor persists despite resolving the shoulder pain or stopping the associated medication, a separate evaluation by a neurologist is necessary.