Why would your sternocleidomastoid muscle be swollen?

Answer 1

Most likely would be a muscle strain from whiplash. Also possible are repetitive motion injuries such as weight lifting or even sitting at the computer for extended periods of time in a non-ergometric position.

A good physical therapist or physician should be able to distinguish between a swollen muscle proper, vs. a lump or mass on top of, or behind, the muscle.

But any number of tumors or abscesses could cause an asymmetrical character of the sternocleidomastoid.

Depending on medical history, bacterial infection, tumor or carotid disorders should be ruled out via blood work/ENT, cat scan, soft tissue scan of anterior neck with contrast, and/or Doppler ultrasound. Check skin over affected area for lesions as it could indicate herpes virus.

Again, though, if the muscle itself is presenting as swollen for the length of one or both heads of the scm, from sternum to mastoid, then it's extremely likely a muscle strain.

In my experience, such strains can present as anomalies with no known cause, and they could resolve very slowly and perplex doctors and therapists alike. If this is the case, keep ruling out scary things, manage the pain any way you can, and wait. A muscle strain in the scm can be extremely painful, scary and debilitating, causing god awful headaches for weeks or months, a choking feeling, hoarseness, anxiety and depression.

If anyone doubts your symptoms or calls you a hypochondriac, show them this and tell them to fluff your pillow.