The study population will include a total of 500 subjects, selected from outpatients accessing the Neurophysiology Service for a neurophysiological study of the upper limbs. Only those whose neurophysiological examination results negative for Peripheral Nervous System pathology (i.e., negative electroneurography and electromyography according to AANEM guidelines) will be recruited. The subjects will be enrolled in 22 centers distributed throughout Italy, with our center planning to recruit 50 subjects.

The diagnostic procedures include electroneurography and electromyography, which are standard clinical practice. Ultrasound (ultrasonographic study) is not an experimental technique but is considered an additional procedure specifically included in the study protocol.

The primary objective of the study is to establish normative values for the CSA of the ulnar nerve and assess the reliability of the measurement through inter-operator comparison (between a physician and a neurophysiology technician). Therefore, during an evaluation lasting approximately 30-60 minutes, the enrolled subjects will undergo an electroneurographic/electromyographic and ultrasound study of the ulnar nerve. The latter will be performed by two independent operators (a physician and a neurophysiology technician).

Inclusion Criteria:

• Over 18 years old EMG/ENG completely negative for pathologies of the peripheral nervous system (ENG and EMG negative according to the regulatory data of each single Center) Signature of the informed consent

Exclusion Criteria:

• Diabetes, Hepatitis, Renal Failure History of NPL or previous CT Previous pathologies of the peripheral nervous system Previous trauma to the limb in question Positive familiarity for neuromuscular disorders

Patients with indication to perform an EMG/ENG for upper limb which fulfill inclusion/exclusion criteria