WebMD lists a number of conditions associated with body shaking, including the flu in adults, viral syndrome and Parkinson's disease. An acute stress reaction or cold exposure also causing body shakes. WebMD also notes several other causes, including coxsackie virus infection and a rare disease called sarcoidosis.
Some of the conditions that WebMD names, such as toxic shock syndrome and cat-scratch disease, have a clear connection to body shaking. However, some of the other conditions, such as lupus, endocarditis and porphyria, may come as more of a surprise. The site also mentions lyme disease, hypothyroidism in adults, bird flu, west Nile virus, ricin poisoning and tick bites as potential causes of body shaking. Drug use, such as cocaine abuse and methamphetamine use, as well as medication side effects sometimes results in body shaking. A benign essential tremor manifests itself as shaking of the hands and forearms along with a quivering voice. However, tremors themselves often indicate other serious medical conditions or that medications are affecting the central nervous system, such as in the cases of Parkinson's disease, liver failure, alcoholism, mercury exposure, arsenic poisoning, lithium and certain antidepressants. Furthermore, WebMD notes that benign essential tremors differ from those that result from a condition such as Parkinson's disease, which makes a difference in treating the tremor or the condition.