A Hidden Presentation of a Common Disease

Endometriosis is widely recognized as a pelvic condition associated with dysmenorrhea, infertility, and chronic pelvic pain. However, its clinical behavior extends far beyond the pelvis. In certain patients, particularly those with advanced disease, endometrial-like tissue can implant on the diaphragm. This form—diaphragmatic endometriosis—often presents with symptoms that appear unrelated to gynecology, leading to frequent misdiagnosis.

One of the most striking and underrecognized presentations is cyclic shoulder pain, a symptom that may initially direct both patients and clinicians toward orthopedic or neurologic causes rather than an underlying systemic disease.

Why the Shoulder? The Anatomical Explanation

The diaphragm is innervated by the phrenic nerve, which originates from cervical spinal roots C3 to C5. These same spinal segments contribute to sensory pathways of the shoulder. When the diaphragm becomes irritated—such as by endometriotic implants undergoing cyclic inflammation—the resulting pain is transmitted through this nerve and perceived in the shoulder.

This phenomenon, known as referred pain, explains why patients may experience right-sided shoulder pain without any primary shoulder pathology. The cyclical nature of the symptoms, often coinciding with menstruation, is a critical diagnostic clue.

Clinical Pattern: What Patients Actually Report

Patients with diaphragmatic endometriosis often describe:

-Recurrent right shoulder pain, frequently worsening during menstruation

-Upper abdominal or right upper quadrant discomfort

-Pain with deep inspiration

-Occasionally, chest discomfort or shortness of breath

What makes this presentation particularly challenging is that pelvic symptoms may be minimal or even absent. As a result, many patients undergo prolonged evaluation for musculoskeletal conditions before the correct diagnosis is considered.

Right-Sided Predominance: An Unresolved Question

A consistent observation in clinical practice is the predominance of diaphragmatic endometriosis on the right side. The most accepted explanation involves the circulation of peritoneal fluid directing endometrial cells toward the right subphrenic space. However, this mechanism has not been definitively proven, and no single theory fully explains this distribution. It is important to acknowledge that this remains an area of ongoing investigation.

Why Diagnosis Is Frequently Delayed

Diaphragmatic endometriosis is often missed due to a combination of factors:

-Symptoms mimic common orthopedic conditions

-Standard imaging protocols are focused on the pelvis

-Conventional ultrasound does not assess the diaphragm

-Lack of awareness of extrapelvic manifestations

Even in patients with known endometriosis, evaluation may stop at the pelvis unless there is a specific reason to investigate further.

The Role and Limitations of Imaging

Diagnostic imaging plays a supportive but imperfect role. Pelvic ultrasound, even when highly specialized, does not visualize the diaphragm and therefore cannot directly detect diaphragmatic lesions. Its value lies in identifying associated pelvic disease, which may raise suspicion for more extensive involvement.

Magnetic resonance imaging offers a broader anatomical field and can sometimes detect diaphragmatic nodules or thickening, particularly in posterior locations. However, small or superficial lesions may still be missed. For this reason, definitive diagnosis often relies on surgical exploration, where the diaphragm must be deliberately and systematically inspected.

A Broader Perspective on Endometriosis

Diaphragmatic involvement reinforces a critical concept: endometriosis is not confined to the pelvis. It is a disease capable of affecting multiple anatomical compartments and producing symptoms that mimic unrelated conditions. Recognizing patterns such as cyclic shoulder pain allows clinicians to move beyond compartmentalized thinking and approach the disease in a more integrated way.

April 2026.