The various causes are carpel tunnel syndrome, inflammation of the tendons of the
arm due to repetitive work, lymphangitis, deep vein thrombosis,
osteoarthritis and rheumatoid arthritis. You need to consult a doctor and rule these out by blood tests, X-rays, nerve conduction studies, rheumatoid factor, ESR, etc. Muscle injury causing the muscles to swell up can be diagnosed by enzymes transaminase (AST) and creatinine phosphokinase. Hope this helps.