@Pyr2 - Well, if your PCR is negative, I doubt you have active EBV to any appreciable degree. During an active phase of infection, you'd see the PCR elevated. I think that in general your illness sounds more autoimmune. RF is raised frequently in autoimmune diseases other than rheumatoid arthritis, and even in healthy people. I wouldn't make too much of it unless you show signs of RA. You can also test ACPA (i.e. CCP) - this is an antibody to cyclic citrullinated peptide, and it is frequently found to be elevated in RA. Neither is a specific finding though, and diagnosis of RA requires evaluation of both clinical and lab markers. You also want to test for inflammation (ESR and CRP). Another, newer, test used for earlier RA is 14-3-3 eta protein - it's often elevated before the others, but is newer and many doctors don't know much about it. I don't think your RF of 13 is indicative of RA from what you are describing. You frequently find much more elevated RF in perfectly healthy people. If your inflammatory markers are negative, and your ACPA is also, I think it's very unlikely.
I wasn't suggesting you have ALPS, only giving an example of a lymphoproliferative disease. They can be autoimmune, but they are often due to somatic mutation.
The symptoms you're describing do not sound like an active viral infection. Your reaction to vaccines, for example, suggests an autoimmune component is more likely (especially given the negative PCR). Antibody titers do not measure virus activity. There is some loose correlation probably, but you cannot make any solid inferences about viral activity based on changes in titers (other than seroconversion, when a person goes from negative to positive). You can sometimes, at best, make educated guesses.
The twitching is an interesting symptom - this implies motor neuron involvement. I have had this too, off and on, generally when it happens it happens for months at a time and then goes away... and then eventually comes back. I've had it start the day of a vaccination. I think this is probably due to some kind of generalized immune effect where all antibodies are increased, and among those there is probably an antibody that is causing your neurological symptoms.
Valcyte is a pretty serious drug, and I'd be hesitant to use it unless I had documented infection. It can have serious side effects. In commonly used doses, valtrex (different drug) is pretty safe, although not quite as effective on EBV or other gamma herpesviruses. If your doctor thinks you need it though due to active infection, the valcyte might make sense. It's definitely possible that some of your symptoms are from that - it is a drug with many side effects. Don't stop it w/o talking to your doctor though - I don't know enough about why you are taking it, and I'm not a doctor! I tend to react poorly to some psych meds (in particlar, low dose TCA's, which are supposed to help ME patients, but I can't tolerate them at all).
A plasma cell dyscrasia refers to the B-lymphocytes (cells which make antibodies). Mature B cells are called plasma cells. So you have a somatic mutation in a B-cell. This frequently results in something called MGUS, or monoclonal gammopathy of undetermined significance. The particular deletion you have is not one of the common ones that I know anything about (there are certain deletions, like q13, that delete certain tumor suppressors and are frequently found in certain cancers, but deletion of the short arm of chromosome 4 doesn't ring any bells for me). What I found from some quick googling was info on germline mutations, but yours is not germline, it's somatic (or you'd have 20/20 cells with it). This means that at some point in your life, a cell mutated, and kept dividing, so all of the cells that are descended from it have the same abnormal genetics. This can be a precursor to many blood cancers, but most people who have MGUS don't develop blood cancers and in fact never even know they have it. I don't think del4q is a high risk deletion, but I'm not that familiar with it.
You really need to have an SPEP and IFE done (serum protein electrophoresis and immunofixation electrophoresis). You should also have your serum free light chains checked. You should have a metabolic panel to check kidney function and possibly a UPEP (urinary protein electrophoresis) to look for monoclonal components in your urine (bence jones proteinuria). These are all tests for pre-malignant or malignant conditions like MGUS (again - even if positive, it's usually not a serious problem, but does need to be monitored).
Your neurological symptoms, combined with the elevated IgM, suggest to me that you also need a workup for monoclonal proteins that could target nerve cells. Anti-MAG (myelin associated glycoprotein) IgM should be checked. This is a monoclonal antibody of type M (always M for some reason, not sure why - not sure anyone knows why). You should also have antibodies to gangliosides checked. I would talk to both a hematologist and a neurologist. The fasciculations (twitching) probably merit an EMG (electromyelogram) or NCS (nerve conduction studies - like an EMG, but with stick ons rather than needles). It doesn't really sound at all like degenerative motor neuron disease - it sounds much more like some type of antibody mediated MGUS kind of syndrome like anti-MAG. The fact that you do have a clone already makes me think you need the workup. Your IgM is not very high though, which suggests the m-spike, if present at all, is not very large. It may be a non-secretory clone, which means it doesn't make antibodies.
I would be surprised though if your hematologist didn't run an SPEP already - although IFE is more sensitive and newer, as are serum free light chains. They don't generally do a bone marrow biopsy before an SPEP!
EBV can infect B-cells and is known to cause mutations in some cases, so it's not impossible that that is what happened with you - but it's also very possible that it just happened randomly. There is always a randomness to somatic mutations. Also, Valcyte has been shown to cause mutations in animals, so considering you already have a monoclonal dyscrasia, I'd only take it if there is strong evidence for an infection that it is treating.
I wouldn't be too panicked, but I do think that what you are describing merits a more thorough workup from a hematologist and a neurologist.
One last thing - the word herx is WAY overused. Be careful whom you listen to on this. People take all kinds of meds for infections and then if they get any symptoms at all they think it's good because it means the med is "working" and call it a herx. There is such a thing as a herxheimer reaction, but it's not nearly as common as people describe, and is generally associated with bacterial infections, especially spirochetes like the bacteria that cause syphilis and lyme disease. A true herx happens within a few hours of taking a drug and is short lived. If you're sick for weeks or months, that's not a herx. You don't get a herxheimer reaction from treating a virus. If you have lyme, and take antibiotics, you could get one.