Sensory neurological examination is an important part of any physical examination. This part of the physical examination takes on even more importance in the workup of the patient with chronic pain. During World War II, Dr. George Riddoch, a neurologist in the British Army, developed a logical approach to the sensory examination with the concept of identifying “signature” surface areas highly correlated with specific anatomic dermatomes, which, in turn, are associated with specific nerve roots. Later, the concept of current perception threshold (CPT) was developed to quantitate level of sensory deficit. Problems developed with this diagnostic technique, however, with significant variability associated with changing skin resistance. Recently, the concept of voltage-actuated sensory nerve conduction (V-sNCT) has resulted in the development of a new instrument to quantitate sensory function.
Conventional EMG (electrical muscle graph) cannot test the nerves causing pain, which is the reason why 40% of patients seek medical help. Only 2% of pain patients have motor nerve symptoms for which EMG is effective. Massachusetts General Hospital Handbook of Pain Management 2005 "EMG/NCV cannot test small pain fibers." "In MOST cases (over 50%) of neck and back pain the anatomic and physiologic diagnosis remains unclear." Neurological Text by Weiner & Goetz Lippinott 2005 "EMG/NCV in the absence of motor symptoms, such as muscle weakness, is costly, time consuming and seldom benefits the patient."
This is the reason 43% of pain patients become chronic and 50% to 80% of back surgeries end in failures. The medical literature does not support that symptoms, physical exams, EMG/NCV or MRI can detect which nerve is causing pain. Only the AXON-II tests pain fibers!
Pain can be Incorrectly Located or Referred
At least 50% of patients misdirect doctors away from the source of pain due to referred symptoms. Over 90% of A-delta fibers reach the sensory cortex so they should allow the patient to exactly localization of the source of pain, but injury causes A-delta fiber to become numb. However, the poor localizing C-Type fiber keep functioning and can even up-regulate. The result is that 50% of patients are so confused they may even localize pain as coming from the opposite side. Guyton states; "This explains why so many patients have serious difficulty localizing the source of pain."