SARS-CoV-2, the virus responsible for COVID-19, caused symptoms that extended beyond the expected respiratory illness. Frequently reported complaints included muscle and joint discomfort. This widespread occurrence of musculoskeletal issues prompted investigation into a direct connection between COVID-19 and localized pain. This article examines the relationship between the infection and pain, focusing particularly on the shoulder area.
Musculoskeletal Pain During Acute COVID Infection
Generalized body aches (myalgia) and joint pain (arthralgia) are common symptoms of an active COVID-19 infection. These musculoskeletal complaints frequently affect the shoulder region. Up to 19% of patients with COVID-19 have reported experiencing myalgia, and arthralgia is also a frequent presentation.
Shoulder pain during the acute phase is often described as a deep ache or stiffness, which may be felt symmetrically. This discomfort is typically one of the earliest symptoms, sometimes presenting within the first few days of the infection. In most cases, this acute musculoskeletal pain is transient, resolving naturally as the body clears the infection.
The presence of shoulder pain, alongside systemic symptoms like fever and fatigue, suggests a broad, body-wide response to the virus. The prevalence and intensity of myalgia and arthralgia in COVID-19 led to a closer look at the underlying biological processes involved. The shoulder, with its complex joint capsule and surrounding muscle groups, is particularly susceptible to these systemic effects.
Biological Mechanisms Causing Joint and Muscle Discomfort
The joint and muscle discomfort during COVID-19 stems from two main biological pathways: the systemic immune response and the potential for direct viral impact. The body reacts to SARS-CoV-2 by producing a massive release of proinflammatory cytokines. This immune overreaction, sometimes called a “cytokine storm,” causes widespread inflammation affecting soft tissues throughout the body.
These inflammatory molecules circulate and directly impact the musculoskeletal system. They contribute to the breakdown of muscle fibers and impair the function of tenocytes, the cells that make up tendons. When this systemic inflammation reaches the shoulder, it causes pain and tenderness by affecting the joint capsule, surrounding tendons, and the bursae.
A second mechanism involves the virus’s ability to enter various cell types, including those in muscle tissue and nerve endings. SARS-CoV-2 uses the angiotensin-converting enzyme 2 (ACE2) receptor to gain entry into cells, and these receptors are present on muscle and synovial tissue. Direct infection of these cells could lead to localized inflammation or neuropathy, resulting in focused pain in the shoulder or arm.
Joint inflammation can also trigger a response mimicking rheumatic conditions, where the body mistakenly attacks its own healthy tissue. This autoimmune-like process leads to joint inflammation visible on medical imaging. The resulting tissue damage and inflammation translate the viral infection into noticeable shoulder and joint pain.
Persistent Shoulder Pain and Long COVID Syndrome
For some individuals, shoulder pain does not resolve after the initial infection, becoming a persistent symptom associated with Long COVID (Post-Acute Sequelae of SARS-CoV-2 infection). This lingering musculoskeletal pain is one of the most common lasting complaints, often continuing for weeks or months. The prevalence of musculoskeletal pain in Long COVID patients is high, sometimes affecting over 10% of those recovering.
The underlying cause of this persistent pain is thought to be a combination of prolonged immune dysfunction and post-viral fatigue syndrome. Chronic, low-grade inflammation can continue long after the acute phase, maintaining the attack on joint and muscle tissues. This sustained systemic stress manifests as localized, ongoing pain in the shoulder and upper back.
Chronic inflammation can lead to specific conditions, such as adhesive capsulitis, commonly known as frozen shoulder. This condition involves the thickening and tightening of the shoulder joint capsule, restricting movement and causing significant pain. Chronic pain may also result from post-viral neuropathy, where nerve damage causes continuous pain signals in the arm or shoulder girdle.
Ruling Out Non-Viral Causes of Shoulder Pain
Shoulder pain is a common complaint with many origins unrelated to a viral infection. When evaluating the source of discomfort, a medical professional will consider non-viral causes that are far more frequent. These include mechanical issues, such as a rotator cuff injury from trauma or repetitive strain, or age-related degeneration like osteoarthritis.
Pain that is clearly localized, worsened by specific movements, and unrelated to systemic symptoms like fatigue or fever is more likely mechanical in nature. Common non-viral causes include bursitis, tendinitis, or nerve entrapment in the neck.
Due to the overlap in symptoms, it is crucial to seek a medical consultation for a differential diagnosis, especially if the pain is severe or limits range of motion. Imaging studies, like MRI or ultrasound, help distinguish between pain caused by viral-induced inflammation and pain arising from structural damage or degenerative changes. Determining the true origin of the pain is the necessary first step toward appropriate management.