Intraepithelial Lymphocytosis: Causes, Symptoms, Treatment

If you’ve ever wondered what your small intestine does all day, the answer is: a lot. It absorbs nutrients,
negotiates with trillions of microbes, and quietly prevents your lunch from becoming an international incident
in your immune system.

Intraepithelial lymphocytosis is what happens when a pathologist looks at a tiny intestinal biopsy
under the microscope and says, “Hmm… there are more lymphocytes (immune cells) hanging out inside the lining
than we usually expect.” Think of it like extra security guards posted inside the “wall” of the intestine.
Sometimes that’s a smart precaution. Sometimes it’s a clue that something else is going on. And sometimes it’s
just… confusingly nonspecific.

This article breaks down what intraepithelial lymphocytosis means, what it can be associated with, what symptoms
people may notice, and how treatment typically works (spoiler: it’s less about “treating a microscope finding”
and more about treating the reason it’s there).

What Is Intraepithelial Lymphocytosis?

Let’s translate the term:

Intraepithelial = within the epithelium (the surface lining of the intestine)

Lymphocytosis = increased lymphocytes (a type of white blood cell)

In many cases, this finding shows up in the duodenum (the first part of the small intestine).
You may also see it described as:

• Duodenal intraepithelial lymphocytosis
• Duodenal lymphocytosis
• Lymphocytic duodenitis or microscopic enteritis
• Marsh 1 lesion (when villi look normal but lymphocytes are increased)

Importantly: this is not a diagnosis by itself. It’s a pattern that can appear for multiple reasons,
ranging from gluten-related disorders to infections, medication effects, immune conditions, or gut “irritation”
from other causes.

How Is It Measured?

Pathologists often count how many intraepithelial lymphocytes (IELs) appear per 100 surface epithelial cells.
Different labs and studies may use slightly different cutoffs, and counting methods can vary (special stains
may be used if the result is borderline). The key takeaway is that it’s a quantitative microscope finding,
not a “yes/no” vibe check.

Why It Matters (and Why It Can Be Tricky)

Intraepithelial lymphocytosis can be an early clue for certain conditionsespecially when paired with symptoms,
blood test results, or additional biopsy features. But it can also show up without major structural damage to
the intestine, and that’s where interpretation gets… spicy.

Here’s why it’s tricky:

• It can be an early stage of a condition (like early celiac disease) before more obvious
  intestinal changes appear.
• It can be a reaction to something else entirely (like an infection or medication).
• It can be incidental in people who had an endoscopy for a different reason.

So when a biopsy report mentions intraepithelial lymphocytosis, clinicians usually ask:
“What’s the most likely underlying cause in this person?”

Common Causes of Intraepithelial Lymphocytosis

Below are common and clinically important categories. Not every cause applies to every person, and some people
have more than one factor at the same time (because the human body loves a plot twist).

1) Gluten-Related Disorders

One of the most discussed associations is celiac disease, an immune-mediated reaction to gluten
that can damage the small intestine. In some people, the earliest biopsy finding may be increased IELs with
otherwise normal villous structure (often described as Marsh 1).

However, increased IELs alone do not confirm celiac disease. Clinicians generally interpret this alongside:

• Blood tests for celiac-related antibodies (and total IgA levels)
• Whether the person is eating a gluten-containing diet at the time of testing
• Symptoms and nutrition markers (like iron or vitamin deficiencies)
• Family history or associated autoimmune conditions
• Sometimes genetic markers that make celiac disease more or less likely

Other gluten-related conditions, like non-celiac gluten sensitivity, may be discussed in some
workups, though diagnosis and mechanisms differ and the biopsy picture can be variable.

2) Infections (Yes, Even the “Boring” Ones)

Certain infections and inflammatory triggers can increase IELs, including:

• H. pylori-associated inflammation (often primarily in the stomach, but it can influence the duodenum)
• Giardia (a parasite that can cause prolonged GI symptoms)
• Viral gastroenteritis or other infectious enteritis (sometimes as a transient change)

If infection is suspected, clinicians may consider stool testing, breath testing, or treatment directed at the
specific cause, depending on the clinical picture.

3) Medications (The “Helpful” Stuff That Occasionally Isn’t)

Some medications are associated with small intestinal irritation or inflammatory patterns that may include
intraepithelial lymphocytosis. Examples that often come up in clinical discussions include:

• NSAIDs (like ibuprofen or naproxen), especially with frequent or long-term use
• Some acid-suppressing medications (depending on context and coexisting issues)
• Certain blood-pressure medications (rare, but discussed in differential diagnosis in some cases)

This doesn’t mean “never take these medications.” It means that if IELs are noted and symptoms persist, it’s
reasonable for a clinician to review medication history and timing.

4) Small Intestinal Bacterial Overgrowth (SIBO) and Gut Microbiome Disruption

SIBO can cause bloating, gas, diarrhea, constipation, or malabsorption in some people. It’s also
discussed as a possible contributor to microscopic inflammatory changes in the small intestine, including
increased IELs in certain contexts.

Workup may include breath testing or empiric management in selected cases, guided by a clinician’s judgment and
symptom pattern.

5) Autoimmune and Inflammatory Conditions

Sometimes intraepithelial lymphocytosis appears alongside autoimmune or inflammatory disorders. Examples that may
be considered in a broader evaluation include:

• Inflammatory bowel disease (like Crohn’s disease)
• Immune deficiency states in certain presentations
• Other autoimmune conditions associated with GI symptoms

In these scenarios, the biopsy is rarely interpreted in isolationsymptoms, labs, imaging, and sometimes additional
biopsies help clarify what’s actually happening.

6) Sometimes: No Single Clear Cause

It’s also possible that intraepithelial lymphocytosis is found and, after reasonable evaluation, no single “smoking gun”
is identified. In those cases, clinicians may focus on symptom management, nutrition, and follow-upespecially if the
person is doing well and there are no red-flag signs.

Symptoms: What People Often Notice

The tricky part: intraepithelial lymphocytosis itself doesn’t “cause” symptomsthe underlying condition does.
Still, many people who have this finding on biopsy are being evaluated for symptoms such as:

Digestive Symptoms

• Chronic or intermittent diarrhea
• Bloating and excess gas (the “I swear my stomach is a balloon” feeling)
• Abdominal discomfort or pain
• Nausea, indigestion, or early fullness
• Constipation (especially if SIBO or other overlapping issues exist)

Whole-Body and Nutritional Symptoms

• Unexplained fatigue
• Iron deficiency anemia (sometimes discovered on routine labs)
• Unintended weight loss (not always present)
• Low levels of certain vitamins/minerals in some cases
• Skin issues or mouth ulcers in specific underlying conditions

Some people have no symptoms and only learn about intraepithelial lymphocytosis because they had an endoscopy
for reflux, anemia, or another evaluation.

How It’s Diagnosed: Putting the Puzzle Together

Intraepithelial lymphocytosis is typically identified on a biopsy taken during an upper endoscopy. But the real
work begins afterward: figuring out the “why.”

Common Next Steps Clinicians Consider

• Celiac blood tests (commonly tissue transglutaminase antibodies with total IgA, and sometimes additional markers)
• Diet context check: Were you eating gluten regularly during testing? (This matters a lot for accuracy.)
• Medication review: Frequency and timing of NSAIDs and other relevant medications
• Infection assessment: Testing or treatment if suspicion is high (stool tests, targeted therapies, etc.)
• Evaluation for overlap conditions: Depending on symptoms, labs, and exam

Specific Example: “Marsh 1” Doesn’t Automatically Equal Celiac Disease

A common scenario looks like this:
Someone has bloating, mild anemia, or chronic diarrhea. Endoscopy shows normal-looking villi, but biopsy shows increased IELs.
The report mentions “Marsh 1” or “lymphocytic duodenitis.”

In that situation, a clinician may:

• Check celiac serology (and confirm gluten exposure at the time)
• Assess for H. pylori or other infection triggers
• Review NSAID use
• Consider SIBO evaluation if symptoms fit
• Look at nutrition labs (iron, B12, folate, vitamin D) if indicated

The goal is not to “treat Marsh 1.” The goal is to treat what’s causing the immune system to crowd the intestinal lining.

Treatment: What Usually Helps

Treatment depends on the underlying cause, symptom severity, and whether there are nutritional deficiencies or other complications.
In many cases, addressing the driver improves symptoms and may also improve biopsy findings over time.

If Celiac Disease Is Diagnosed

The cornerstone treatment is a strict gluten-free diet. This typically includes:

• Education on hidden gluten sources (sauces, seasoning blends, cross-contact)
• Nutrition support to ensure balanced intake (not just “swap bread and call it a day”)
• Follow-up labs to monitor recovery and deficiencies
• Sometimes repeat endoscopy in selected situations (especially if symptoms persist)

Practical tip: If celiac disease is still being evaluated, clinicians often advise not starting a gluten-free diet yet,
because removing gluten can make tests less reliable.

If an Infection Is Identified

Treatment may include targeted therapy, such as:

• Eradication therapy for H. pylori when present and clinically relevant
• Antiparasitic treatment if Giardia is confirmed
• Supportive care and follow-up if a transient infection is suspected

If Medications Are Suspected Contributors

A clinician may recommend:

• Reducing or stopping NSAIDs when possible (and using alternatives when appropriate)
• Reassessing the need for certain long-term medications
• Monitoring symptoms after medication changes

Never stop a prescribed medication on your ownespecially if it’s for heart, blood pressure, or other essential conditions.
The point is coordination, not chaos.

If SIBO or Functional Overlap Is Suspected

Management may include:

• Breath testing or clinician-guided evaluation
• Targeted treatment (which may include antibiotics in some cases)
• Diet strategies tailored to symptoms (not a one-size-fits-all food ban list)
• Addressing contributing factors (motility, anatomy, other GI conditions)

General Supportive Care That Often Matters

• Correcting deficiencies (iron, B vitamins, vitamin D) if present
• Hydration and fiber strategy appropriate to diarrhea vs constipation patterns
• Tracking triggers in a short, structured way (no need to become a full-time spreadsheet)
• Follow-up if symptoms persist, worsen, or red flags appear

When to Seek Prompt Medical Care

If you have intraepithelial lymphocytosis plus any of the following, don’t “wait it out” indefinitelyget evaluated:

• Unintentional weight loss
• Blood in stool or black/tarry stools
• Persistent vomiting
• Severe abdominal pain
• Signs of dehydration
• Worsening anemia or nutritional deficiency symptoms

Frequently Asked Questions

Is intraepithelial lymphocytosis the same thing as celiac disease?

No. It can be associated with celiac disease, especially early on, but it also occurs with infections, medications, and other conditions.
Diagnosis usually requires combining biopsy results with blood tests, diet context, and clinical symptoms.

Can it go away?

Often, yesespecially if the underlying cause is found and treated (such as an infection or a medication trigger). In other cases, it may persist,
which is why follow-up planning matters when symptoms or deficiencies continue.

What should I ask my clinician if my biopsy shows this?

• What are the most likely causes in my case?
• Were my celiac blood tests done while I was eating gluten regularly?
• Should we evaluate for infection, medication effects, or SIBO?
• Do I have any vitamin/mineral deficiencies we should address now?
• What symptoms or lab changes should trigger re-evaluation?

Real-Life Experiences: What People Commonly Describe (Plus a Few Hard-Won Lessons)

The weird thing about intraepithelial lymphocytosis is that it often lands people in a medical “in-between.”
It’s not the dramatic biopsy result with obvious damage that screams a single answer. It’s more like your intestine
left a sticky note that says: “Something annoyed me. Please investigate.”

Many people describe the frustration of vague symptoms long before the biopsy:
bloating that doesn’t match what they ate, bathroom habits that swing like a pendulum, fatigue that feels like
walking through wet cement, or iron levels that keep dropping even though they’re “doing everything right.”
When the biopsy finally comes back with a fancy phrase, the first reaction is often reliefbecause at least the
symptoms weren’t imaginary. The second reaction is usually: “Okay… so what does this actually mean?”

A very common experience is the gluten question. Some people are told, “This could be early celiac disease,”
and immediately want to throw gluten out like it’s a houseguest who never leaves. Understandable. But many also discover
(sometimes the hard way) that going gluten-free too early can make testing less clear. People often wish they had been told:
“Before you change your diet dramatically, make sure the diagnostic plan is complete.” It’s not about delaying reliefit’s about
avoiding a forever-diagnosis based on half the evidence.

Another theme: medication surprises. Plenty of folks don’t think of over-the-counter pain relievers as something that
could affect the gut lining, because they’re so common. Then they connect the dots: a period of frequent NSAID use for headaches,
workouts, or chronic pain… followed by stomach discomfort, loose stools, or worsening reflux… and then the biopsy finding.
When medication changes help, it can feel like winning a very small but satisfying battle against the universe.

People who end up having an infection (like H. pylori or Giardia) often describe a different journey: symptoms that are persistent,
annoying, and oddly resistant to generic “eat bland food” advice. There’s a particular kind of vindication in learning that the problem
had a name, a test, and a targeted treatmentespecially after months of feeling like your stomach is improvising its own rules.

And then there’s the group that doesn’t get a neat answer right away. They often describe the emotional roller coaster of
“not serious enough to be obvious, not mild enough to ignore.” In those cases, people tend to do best with a practical approach:
tackle deficiencies, keep a short symptom log, avoid turning eating into a fear-based scavenger hunt, and work with a clinician to
test the most likely causes first. If you’re in this camp, it may help to remember: a nonspecific biopsy finding does not mean nothing’s wrong
it means your healthcare team has to match the microscope clue to the bigger story.

The most consistent “lesson learned” people share is also the least dramatic:
progress usually happens when the plan is organized.
One step at a timeconfirm or rule out celiac appropriately, review meds, consider infection and overgrowth when symptoms fit,
and support your body while the detective work is happening. Not glamorous, but neither is spending the afternoon arguing with your gut.

Conclusion

Intraepithelial lymphocytosis is a meaningful clue, but it’s rarely the final answer. It typically signals that the intestinal immune system is
reacting to somethingoften a gluten-related disorder, infection, medication effect, microbiome disruption, or inflammatory condition.
The best outcomes usually come from pairing biopsy findings with targeted testing, careful history (especially diet and medications),
and treatment aimed at the underlying cause rather than the microscope label.