Pain, particularly shoulder pain, is a social and economic problem worldwide. Although visceral pathology is not yet taken into account in the diagnosis of these pains, it is likely that on numerous occasions the hepatobiliary visceral condition causes referred pain in the metameric area belonging to the shoulder due to the involvement of the phrenic nerve. Therefore, the aim of this project is to study the response of treatment by neuromodulation of the phrenic nerve for shoulder pain in patients with associated hepatobiliary pathologies, assessing the possible visceral involvement in the symptomatology.

Approximately 80% of patients with liver disease suffer chronic pain and fatigue, which can lead to sensitization of the central and peripheral nervous system. Central sensitization is an increase in the responsiveness of neurons within the central nervous system, which can lead to generalized pain hypersensitivity. It has been shown that some lesions or inflammatory processes can trigger changes in the nervous system, generating persistent pain.

According to the theory of visceral referred pain, there are visceral and musculoskeletal stimuli that converge in higher centers capable of producing referred pain in regions where metameric innervation is shared. This raises the possibility that altered visceral mechanisms may provoke and chronify musculoskeletal pain.

According to this theory, people with structural or functional hepatobiliary pathologies may have referred pain in the right metameric territory of C2-C3-C4-C5, which may generate pain in the shoulder on the same side. This is due to the fact that the phrenic nerve sensitively innervates Glisson's capsule, so any affectation of this structure can generate afferent stimuli to the previously mentioned metameric levels.

The phrenic hypothesis plays a very important role today, having as its main "endorsement" the analgesic techniques of phrenic blockade used for shoulder pain after hepatectomy. In order to eliminate this post-operative shoulder pain, electrical or medical nerve blocks are used.

Inclusion Criteria:

• Over 18 years of age.
• Subjects presenting right shoulder pain at the time of enrollment in the study.
• Presentation of a hepatobiliary visceral disorder that may justify the visceral etiology of the pain.
• That they agree to participate in the project by signing the informed consent form.

Exclusion Criteria:

• Patients with chronic pain due to other diseases such as malignant disease.
• Patients with rheumatic diseases.
• Cutaneous infection in the area of pain.
• Disease of neurological, traumatic, oncologic, or infectious origin that rules out the visceral origin of the pain.
• Uncooperative subject.
• Severe psychiatric disease.
• Loss of cognitive capacity.
• Contraindication to electrotherapy.