Could a nickel-size hard knot on the back of my neck be something besides cyst?

It is possible that a nickel-size hard knot on the back of your neck could be something besides a cyst. Other possibilities include:

- Lipoma: A lipoma is a benign, fatty tumor that can grow anywhere on the body, including the neck. Lipomas are usually soft and movable, and they do not typically cause pain.

- Swollen lymph node: Lymph nodes are small, bean-shaped glands that help to filter out bacteria and other foreign substances from the body. When lymph nodes become swollen, they can feel like hard knots. Swollen lymph nodes can be caused by a variety of infections, including the common cold and flu, as well as more serious conditions such as cancer.

- Muscle strain or sprain: A muscle strain or sprain can occur when the muscles or ligaments in the neck are overstretched or torn. This can cause pain, swelling, and tenderness.

- Skin cancer: In rare cases, a hard knot on the back of the neck could be a sign of skin cancer. Skin cancer can appear in a variety of forms, including as a hard, painless lump.

If you are concerned about a hard knot on the back of your neck, it is important to see a doctor for evaluation. The doctor will be able to determine the cause of the knot and recommend the appropriate treatment.