There are many electrodiagnostic tests used to make a diagnosis of CTS, but the most sensitive, specific, and reliable test is the Combined Sensory Index (also known as the Robinson index). Electrodiagnosis rests upon demonstrating impaired median nerve conduction across the carpal tunnel in context of normal conduction elsewhere. It is often stated that normal electrodiagnostic studies do not preclude the diagnosis of carpal tunnel syndrome. The rational for this is that a threshold of neuropathy must be reached before study results become abnormal and also that threshold values for abnormality vary. Others contend that idiopathic median neuropathy at the carpal tunnel with normal electrodiagnostic tests would represent very, very mild neuropathy that would be best managed as a normal median nerve. Even more important, notable symptoms with mild disease is strongly associated with unhelpful thoughts and symptoms of worry and despair. Notable CTS with unmeasurable IMNCT should remind clinicians to always consider the whole person, including their mindset and circumstances, in strategies to help people get and stay healthy. Imaging
The role of MRI or ultrasound imaging in the diagnosis of idiopathic median neuropathy at the carpal tunnel (IMNCT) is unclear. Their routine use is not recommended. MRI has high sensitivity but low specificity for IMNCT. High signal intensity may suggest accumulation of axonal transportation, myelin sheath degeneration or oedema. Differential diagnosis
There are few disorders on the differential diagnosis for carpal tunnel syndrome. Cervical radiculopathy can also cause paresthesia abnormal sensibility in the hands and wrist.
Parasystole is a kind of arrhythmia caused by the presence and function of a secondary pacemaker in the heart, which works in parallel with the SA node. Parasystolic pacemakers are protected from depolarization by the SA node by some kind of entrance block. This block can be complete or incomplete. Parasystolic pacemakers can exist in both the atrium or the ventricle. Atrial parasystolia are characterized by narrow QRS complexes
Two forms of ventricular parasystole have been described in the literature, fixed parasystole and modulated parasystole. Fixed ventricular parasystole occurs when an ectopic pacemaker is protected by entrance block, and thus its activity is completely independent from the sinus pacemaker activity. Hence, the ectopic pacemaker is expected to fire at a fixed rate. Therefore, on ECG, the coupling intervals of the manifest ectopic beats will wander through the basic cycle of the sinus rhythm. Accordingly, the traditional electrocardiographic criteria used to recognize the fixed form of parasystole are:

the presence of variable coupling intervals of the manifest ectopic beats;
inter-ectopic intervals that are simple multiples of a common denominator;
fusion beats.According to the modulated parasystole hypothesis, rigid constancy of a pacemaker might be expected if the entrance block were complete, but if there is an escape route available for the emergence of ectopic activity, then clearly there must be an effective ionic communication, not complete insulation, between the two tissues. If there is an electrical
communication between the two, then the depolarization of the surrounding ventricle may influence the ectopic pacemaker.