Most of the people who have pains in the joints have them because of arthritis (but see symptoms of other types of joint pains). The pains usually strike first in the outer joints like wrists, carpels, fingers or joints with a history of injury. Load bearing joints are also vulnerable. The pain is most likely in the early morning. It is often accompanied by stiffness. It is not to be assumed that the disease is localized because the pain is, Arthritis is present throughout the body and can affect kidneys, pericardium of the heart, and connecting tissue [Strukov][Ropes]. It is a disease largely associated with humans [LaMont-Havers], probably partly because animals can not talk (or in the case of rodents possibly because they make no use of cortisol), but I suspect primarily because animals usually do not have access to refined food.
Arthritis has few externally observable symptoms, especially in early stages. There are no known consistent biochemical changes in arthritis (which word in these articles will be equated with "rheumatoid arthritis" or RA) except a lower cellular potassium content than normal [LaCelle][Sambrook], and a somewhat higher plasma copper content along with a protein which binds the copper in the serum [Schubert]. However there are reports of some changes, which show up in a high proportion of arthritics.
There have been reports of low potassium (the only consistent difference from normal they found) [Syrjanen], calcium, phosphorus, lysozyme, and IgA peptide in the saliva of juvenile arthritics [Siamopoulou et al] (which form of arthritis could be similar to the adult form). The sodium/potassium ATPase activity is lower in erythrocyte (red blood cell) membrane [Masoon-Yasinzai] and lower than in normal, osteoarthritis, or gout [Testa]. The steroid hormone dehydroepiandrosterone sulfate (DHEA) is statistically lower in arthritics [Dessein] as is cortisol and pregnanediol, even though ACTH is higher, as is aldosterone [Khetagurova]]. The aldosterone being higher suggests that there is something besides the low potassium itself that is involved in the cause of arthritis since aldosterone stimulates excretion of potassium and has a positive feedback. The ratio of IL6 peptide immune hormone to cortisol is statistically correlated to number of swollen joints and low grip strength. There has been an effort to use changes in some of the body's other proteins in diagnosis, but with limited success so far, although some of the other rheumatic diseases can be almost diagnosed from blood proteins alone [Waller].
As nearly as I can tell most of the above seemed to be the consensus for arthritis at the 1982 Pan American Conference on Arthritis and largely remains so today. Erythrocyte sedimentation rate (ESR) is poor for diagnosis [There are significant correlations between IgM RF and IgA immune proteins and a higher disease activity [Chen] but the correlations are not perfect. There is lower glycosylation of immune peptides (addition of sugar molecules) during arthritis [Axford]. I do not know what the significance of this is although addition of sugars may prevent the peptides from being normally active. C3 and C4 compliments are said to be the best of the other discriminators [Sari, et al]. In epithelial sodium channels, alpha and beta subunits are higher than normal in rheumatoid arthritis but not present in osteoarthritis [Trujillo, et al]. There is high activity of collagenase and elastase in the synovial fluid of patients with rheumatoid arthritis, which is about 30 times higher than that found in the synovial fluid of patients with osteoarthritis [Bazzichi]. Arthritis sometimes has fatigue associated with it. The settling rate red blood cells is different in arthritis.
