First of all I am sorry to hear that you have a lytic lesion on your skull. Anytime there is an abnormal finding on exam, or through medical testing it can raise many different questions that insight anxiety about what might have caused the abnormal finding/result. I am not saying that this is exactly what you are going through, but this can be a very common response by people in these situations, so if you feel this way it is completely normal.
Lytic lesions refer to the appearance of the bone on an X-ray
(typically a helical X-ray called a CT scan). Specifically "lytic" lesions are areas that have a small amount of bone missing in a particular area. They can be found in isolation, or can be multiple. There are many different things that can cause lytic lesions of bone. Also lytic lesions are not only found on the skull, but can be found on many of the bones within the body. I am sure that you have read some on the Internet and found some information about multiple myeloma which is one of the classic disease processes that can cause lytic bone lesions. However there are actually multiple processes that can cause lytic lesions one the bone. Whether it be from pressure directly on the bone from a mass lesion, or a less focal cause like a metabolic or hormonal cause. You have given some information about your work-up with some abnormal findings like an elevated ANA and Sed rate which are non-specific markers that tell me that you have some sort of an inflammatory process somewhere in your body. I would definitely recommend that you continue to pursue a thorough work-up with a second opinion, especially If you are dissatisfied with the opinion you got from neurosurgeon
you saw. You may need to go back to your primary care physician
and ask who they may recommend as a referral for a second opinion (this is sometimes needed for insurance approval). I would recommend discussing this with your primary care physician. I hope that this is helpful.