Diagnosing Mooren Ulcer: The Process of Exclusion

Diagnosing Mooren ulcer is a meticulous clinical process. Because there is no single blood test or biopsy that can “prove” a person has Mooren ulcer, doctors must instead rule out other conditions that cause similar ulcers ^[1][2].

In medical terms, this is called a diagnosis of exclusion ^[1]. If an eye ulcer looks like Mooren but a cause is found—such as an infection or an autoimmune disease—it is not Mooren ulcer, but rather a condition that mimics it ^[1][3].

The Look-Alikes: Systemic PUK and Infections

The physical appearance of a Mooren ulcer—a crescent-shaped melting at the edge of the cornea—is shared by a group of conditions known as Peripheral Ulcerative Keratitis (PUK) ^[4][3].

When PUK is caused by a systemic (body-wide) disease, it is called PUK associated with systemic disease (historically referred to as “pseudo-Mooren ulcer”) ^[1][5]. Distinguishing between true Mooren and systemic PUK is critical because the treatments differ. The most common “look-alikes” include:

1. Systemic Autoimmune Diseases: Conditions like Rheumatoid Arthritis (RA) and Granulomatosis with Polyangiitis (GPA) are the most frequent causes of systemic PUK ^[6][7]. In some people, the eye ulcer is the very first sign of the disease, appearing before the patient feels sick or has joint pain ^[6].
2. Infections: Viruses (like Herpes Simplex), bacteria, syphilis, and tuberculosis can all cause ulcers on the edge of the cornea ^[8][9]. Using steroid drops on an undiagnosed infection can make the condition much worse, so assessing for infection is urgent ^[10].

The Diagnostic Process

To reach a Mooren ulcer diagnosis, your medical team will perform a comprehensive evaluation guided by your history, exposures, and examination. There is no single mandatory panel that rules out systemic disease, and testing is individualized.

The Eye Exam (Slit-Lamp)

Your specialist will use a high-powered microscope called a slit lamp to look for clues, such as the presence or absence of scleritis (inflammation of the white part of the eye) ^[2][3].

• Systemic PUK: Often involves the white part of the eye (scleritis or episcleritis). The presence of scleritis can support an associated systemic disorder ^[2].
• Mooren Ulcer: Usually “spares” the white part of the eye, but the absence of scleritis does not definitively establish Mooren ulcer ^[1]. The overall clinical picture is required.

Evaluating for Infection

Infection must be assessed urgently. The doctor may gently swab the ulcer or take a small sample (scraping) to send to a lab ^[8][9]. They use PCR (a highly sensitive way to find viral DNA) to check for herpes or other viruses ^[11][8]. Because a rapidly thinning cornea is an emergency, your specialist may treat for presumed sterile inflammation, infection, or both simultaneously without waiting for every test result ^[10]. Never start, stop, or change steroid drops on your own, as they can worsen infections.

Blood Work and Imaging

To look for hidden autoimmune markers, a series of blood tests is often ordered based on your specific case ^[1]. This may include:

• ANCA Testing: To look for vasculitis ^[12].
• RF and Anti-CCP: To check for Rheumatoid Arthritis ^[13].
• Inflammatory Markers: Such as ESR and CRP ^[14].
• Imaging: A chest X-ray or CT scan may be ordered to look for signs of disease in the lungs, guided by your symptoms ^[12][13].

A diagnosis of Mooren ulcer is supported when reasonable infectious and systemic causes have been excluded ^[1]. Because eye ulcers can occasionally precede a systemic diagnosis, negative bloodwork does not rule out early systemic disease forever. Your doctor may recommend a consultation with a rheumatologist and will reassess your diagnosis if new systemic symptoms appear ^[6][7].