What are the reasons why a thickened Sternocleidomastoid (SCM) muscle would cause pain?

From the Guidelines

A thickened sternocleidomastoid muscle can cause pain due to muscle strain, overuse, or compression of nearby structures, leading to inflammation, microscopic tears, and radiating pain. The most common reasons for a thickened sternocleidomastoid muscle to cause pain include muscle strain or overuse, which results in inflammation and microscopic tears in the muscle fibers, leading to pain and tenderness 1. Additionally, torticollis (wry neck) can develop when the muscle contracts and shortens abnormally, causing the head to tilt toward the affected side while the chin rotates to the opposite side. Myofascial pain syndrome may also occur, characterized by trigger points within the muscle that refer pain to other areas of the neck and head.

Some key points to consider when evaluating the cause of pain from a thickened sternocleidomastoid muscle include:

• Muscle strain or overuse
• Torticollis (wry neck)
• Myofascial pain syndrome
• Cervical dystonia, a neurological condition causing involuntary muscle contractions
• Compression of nearby structures like nerves and blood vessels, leading to radiating pain, numbness, or tingling

It's also important to note that the nerve supply to the breast is from the anterolateral and anteromedial branches of the intercostal nerves from T3 to T5, and irritation anywhere along their course can lead to breast or nipple pain 1. However, the sternocleidomastoid muscle is not directly related to the breast, and its thickening is more likely to cause pain in the neck and head region.

In terms of treatment, physical therapy, muscle relaxants like cyclobenzaprine, anti-inflammatory medications such as ibuprofen, heat/cold therapy, and gentle stretching exercises may be necessary 1. For severe cases, trigger point injections with lidocaine or botulinum toxin may be necessary. Addressing poor posture and ergonomics is essential for long-term management and prevention of recurrence.

From the Research

Thickened Sternocleidomastoid and Pain

The relationship between a thickened sternocleidomastoid muscle and pain can be understood through various mechanisms:

• Overactivity of the sternocleidomastoid muscle is often associated with chronic neck pain (CNP) 2
• A thickened sternocleidomastoid muscle may lead to reduced range of motion, increased disability, and endurance, contributing to pain 2
• The sternocleidomastoid muscle plays a crucial role in neck movement, and its overactivity can disrupt normal movement patterns, leading to pain and discomfort 2
• Interventions such as stretching and massage targeted at the sternocleidomastoid muscle have been shown to reduce pain, disability, and improve range of motion and endurance in individuals with CNP 2

Potential Causes of Pain

Some potential causes of pain associated with a thickened sternocleidomastoid muscle include:

• Increased tension in the muscle, leading to strain on surrounding tissues and joints 2
• Reduced blood flow and oxygenation to the muscle, leading to inflammation and pain 2
• Altered movement patterns and biomechanics, leading to abnormal stress and strain on the muscle and surrounding tissues 2