Endometriosis is a chronic condition characterized by the growth of tissue similar to the lining of the uterus outside of the uterine cavity. This displaced tissue reacts to hormonal changes throughout the menstrual cycle, thickening and bleeding. Since this blood and tissue has no way to exit the body, it causes inflammation, scarring, and the formation of painful adhesions that bind organs together. While typically associated with the pelvic region, endometriosis is now recognized as a systemic disorder, and it can cause upper abdominal pain, though this presentation is rare.
Understanding Classic Endometriosis Pain
The vast majority of endometriosis cases affect the pelvic organs and surrounding structures. The most frequent complaint is dysmenorrhea, or intensely painful periods, which is often described as far more severe than typical menstrual cramping. This pain can begin days before menstruation and extend throughout the entire period.
Endometriosis often causes chronic pelvic pain that persists even outside of menstruation, along with pain during sexual intercourse, known as dyspareunia. Lesions that implant on or near the bowel or bladder can trigger painful bowel movements (dyschezia) or painful urination (dysuria), especially during the menstrual cycle. These symptoms, centered in the lower abdomen and pelvis, are the usual indicators that prompt a diagnosis.
Diaphragmatic Endometriosis and Direct Upper Pain
When the endometrial-like tissue grows on the diaphragm, the condition is called Diaphragmatic Endometriosis (DE). This is a rare form of the disease, estimated to occur in only about 1% to 1.5% of individuals with endometriosis. The presence of these lesions directly on the diaphragm is a primary cause of true upper abdominal pain related to the condition.
The symptoms of DE frequently manifest as pain in the chest, upper abdomen, and the shoulder or neck. This shoulder pain is a telling sign because the phrenic nerve, which supplies the diaphragm, shares nerve pathways with the shoulder and neck. This pain is often cyclical, worsening before or during menstruation as the tissue on the diaphragm swells and bleeds in response to hormones.
In a majority of reported cases, the endometrial lesions are found on the right side of the diaphragm. This right-sided dominance means the upper abdominal pain is typically felt on the right, sometimes mimicking gallbladder issues. The proposed mechanisms for how these cells travel from the pelvis to the diaphragm include retrograde menstruation or spread through the blood vessels or lymphatic system.
Indirect Mechanisms of Upper Abdominal Discomfort
Upper abdominal discomfort linked to endometriosis does not always involve lesions physically present on the diaphragm. One indirect mechanism is referred pain, where the extensive inflammation and scarring in the pelvis irritate nearby nerves. This irritation can lead to the sensation of pain being transmitted and felt in a different, higher location.
Studies suggest that 50% to 70% of those with endometriosis also meet the criteria for Irritable Bowel Syndrome (IBS). The systemic inflammation associated with endometriosis can disrupt gut motility and the microbiome, leading to symptoms like bloating, gas, and cramping that are often felt in the upper digestive tract.
A further connection exists with Small Intestinal Bacterial Overgrowth (SIBO). SIBO is frequently found in people with IBS and can cause significant upper abdominal bloating, distension, and discomfort. The digestive symptoms of endometriosis are so common that many women are initially misdiagnosed with a functional GI disorder before their underlying condition is identified.
Diagnosing and Treating Atypical Endometriosis Symptoms
Diagnosing atypical presentations, particularly those involving the upper abdomen, often proves challenging. Clinicians must maintain a high suspicion for diaphragmatic involvement, especially when upper abdominal or shoulder pain is cyclical and correlates with menstruation. Standard pelvic imaging is unlikely to detect lesions on the diaphragm, necessitating specialized diagnostic tools.
While a definitive diagnosis of endometriosis, regardless of location, still requires laparoscopy with tissue biopsy, specialized imaging like Magnetic Resonance Imaging (MRI) is used to evaluate the diaphragm and other upper abdominal structures before surgery. If diaphragmatic lesions are found, treatment typically involves surgical excision, which may require a specialized surgical approach. Management also involves addressing the indirect causes of discomfort, such as treating co-occurring SIBO or IBS with dietary changes or targeted medications to reduce systemic inflammation and alleviate upper GI symptoms.