The diagnosis of spinal stenosis begins with a complete medical history and physical examination. Your doctor will determine what symptoms are present, what makes them better or worse, and how long they have been present for. A physical examination is essential for determining how severe the condition is, and whether or not it is causing weakness or numbness in certain parts of the body. Abnormalities in the strength and sensation of particular parts of the body that are found with a neurological examination provide the most objective evidence of chronic nerve root compression caused by spinal stenosis. The examination is also used to rule out other conditions such as those associated with hip and knee arthritis or diabetes.
There are no laboratory tests that can detect the presence or absence of a stenosis, but they may be helpful in the diagnosis of unusual causes of nerve root and spinal cord dysfunction. MR scanning or CT scanning can visualize the canal where the nerves live and quantify the degree of narrowing as well as rule out other causes.
Source : back.com