Dyspepsia and irritable bowel syndrome are generally considered separate functional disorders with unknown causes. FD (functional dyspepsia) is associated with upper-gut symptoms while IBS (irritable bowel syndrome) is associated with lower gut symptoms. Both have links to low-grade inflammation.

Crohn’s is a chronic inflammatory disease that can affect any part of the gut – upper or lower.

My hypothesis proposes that Mycobacterium avium subsp. paratuberculosis (MAP) is a major cause functional dyspepsia, irritable bowel syndrome and Crohn’s disease and contends that the only differences between FD, IBS and CD, with regard to MAP as a cause, is the site of infection (upper or lower gut, for example) and the level of inflammation - IBS/FD (low grade inflammation) or CD (chronic inflammation).

It's further proposed that, in some cases, both upper and lower gut may become infected, potentially leading to individuals with both FD and IBS.

Below are 15 hyperlinks to various study summaries that demonstrate associations and similarities between FD, IBS, and CD. For example:

• "A high proportion of Crohn's disease patients show upper gastrointestinal tract involvement"
• "There is a significant prodromal period before the time of diagnosis of Crohn's disease"
• "The authors believe that inflamed bowel disease and at least a subset of irritable bowel syndrome patients exist at two ends of the same spectrum of pathophysiology"
• "Irritable bowel syndrome-like symptoms were found in one-third of ulcerative colitis patients and in 42% of Crohn's disease patients"
• "About half of the FD patients fulfill the Rome II criteria for IBS"
• "Overlapping upper and lower gastrointestinal symptoms in irritable bowel syndrome patients with constipation or diarrhea"
• "The continuously increased risk of IBD detection in IBS patients favors a true association between IBS and IBD."

Links Between Crohn’s Disease and Functional Dyspepsia

Accumulation of Mast Cells and Macrophages in Focal active Gastritis of Patients with Crohn's Disease

Our findings indicated that the diagnosis of focal active gastritis, using immunostain for mast cells and macrophages, is the histological hallmark of gastric Crohn's disease.

High Incidence of Upper Gastrointestinal Tract Involvement in Crohn's Disease

Thus, a high proportion of Crohn's disease patients show upper gastrointestinal tract involvement, with the major involvement in the antrum.

Links Between Irritable Bowel Syndrome and Crohn’s Disease (IBD)

Detection of Colorectal Tumor and Inflammatory Bowel Disease During Follow-up of Patients with Initial Diagnosis of Irritable Bowel Syndrome

...the excess risk of IBD after an initial diagnosis of IBS was cumulatively increased during all the follow-up period. The continuously increased risk of IBD detection in IBS patients favors a true association between IBS and IBD.

Identification of a Prodromal Period in Crohn's Disease but not Ulcerative Colitis

Some of the residual symptoms in subjects treated with Crohn's disease and ulcerative colitis are thought to be related to irritable bowel syndrome… There is a significant prodromal period before the time of diagnosis of Crohn's disease..

Inflammatory Bowel Disease and Irritable Bowel Syndrome: Separate or Unified?

Both irritable bowel syndrome and inflammatory bowel diseases share symptoms of altered bowel habits associated with abdominal pain or discomfort.

Inflammatory Bowel Disease and Irritable Bowel Syndrome

This article contends that many people have both irritable bowel syndrome and inflammatory bowel disease.

Is Irritable Bowel Syndrome a Low-Grade Inflammatory Bowel Disease?

The authors believe that inflamed bowel disease and at least a subset of irritable bowel syndrome patients exist at two ends of the same spectrum of pathophysiology, which involves immune activation and inflammation.

IBS-like Symptoms in Patients with Inflammatory Bowel Disease in Remission; Relationships with Quality of Life and Coping Behavior

Using the Rome II criteria, irritable bowel syndrome-like symptoms were found in one-third of ulcerative colitis patients and in 42% of Crohn's disease patients in remission.

Links Between Functional Dyspepsia and Irritable Bowel Syndrome

Intolerance to Visceral Distension in Functional Dyspepsia or Irritable Bowel Syndrome: an Organ Specific Defect or a Pan Intestinal Dysregulation?

In patients with concomitant symptoms of FD + IBS, gastric and rectal intolerance to distension were present respectively in 82 and 91% patients.

Increased Prevalence of Irritable Bowel Syndrome in Patients with Gastroesophageal Reflux

There is a higher prevalence of IBS in subjects with GERD compared with subjects without GERD.

Epidemiology of Gastroesophageal Reflux Disease: a General Population-Based Study in Xi'an of Northwest China

The etiology and pathogenesis of GERD are probably associated with FD, IBS, and some respiratory…

Impact of Coexisting Irritable Bowel Syndrome on Symptoms and Pathophysiological in Functional Dyspepsia

About half of the FD patients fulfill the Rome II criteria for IBS.

Overlapping Upper and Lower Gastrointestinal Symptoms in Irritable Bowel Syndrome Patients with Constipation or Diarrhea

Upper GI symptoms consistent with functional dyspepsia were more frequent in IBS-C. Although there was considerable overlap of upper and lower GI symptoms in patients with IBS-C and IBS-D, the former had more frequent lower abdominal pain and bloating.