Recent clinical Guideline of Irritable Bowel Syndrome

One in four people; this is the prevalence of functional gastrointestinal disorders

Including irritable bowel syndrome (IBS) and IBS-related syndrome (including functional constipation, functional diarrhea, and functional abdominal bloating).

Functional gastrointestinal disorders are reported to account for about 30% of all patients who visit gastroenterology clinic, thus recently receiving increased attention. Functional gastrointestinal disorders are now recognized as disorders of gut-brain interaction. IBS is diagnosed by Rome IV criteria. That is; Recurrent abdominal pain on average at least 1d/wk in the last 3 mo, associated with 2 or more of the following 3 criteria;

  • Related to defecation
  • Associated with a change in the frequency of stool
  • Associated with a change in the form of stool.

The criteria should be fulfilled for the last 3 months with symptoms onset at least 6 months before diagnosis. Although bloating is a commonly reported symptom, its presence is not mandatory to diagnose IBS.

According to the patients’ predominant stool form on days in which stools are perceived to be abnormal, IBS is characterized by 4 distinct subtypes: IBS-D (diarrhea), IBS-C (constipation), IBS-M (mixed), and IBS-U (no significant pattern). This subtyping is critical to the proper selection of diagnosis studies and treatments, although more than half of patients with IBS change predominant subtypes over a 1-year period. Current pharmacological therapies only target diarrhea and constipation subtypes.

Since there are no distinct biomarkers for IBS, making diagnosis depends on above Rome IV criteria, which is established in 2016. American Journal of Gastroenterology published 2021 guideline for IBS, which incorporates several new evidences thanks to the development of science research. Some of these are herein introduced.

In patients with IBS-D, serologic testing is recommended to rule out celiac disease. These tests include IgA tissue transglutaminase and a quantitative IgA level. Also, in patients with IBS-D, combination of fecal calprotectin and serum C-reactive protein can be used to rule out inflammatory bowel diseases (IBD).

In patients who is from developing countries or poor water quality, it is also recommended to check parasites infection, especially Giardia. Tests include fecal immunoassays or PCR. While bacterial and viral gastroenteritis are acute and associated with alarm symptoms, parasitic infections range from asymptomatic to chronic symptoms of bloating, diarrhea, and abdominal pain similar to IBS. Exposure to Giardia is also associated with the development of food intolerance.

As for the treatment, there may be some beneficial effect, but currently scarce evidence supports for either low FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet or use of any strain of probiotics. On the other hand, soluble, but not insoluble, fiber is recommended to treat global IBS symptoms. Soluble fiber is found in psyllium, oat bran, barley, and beans, while insoluble fiber is found in wheat bran, whole grain and some vegetables. Soluble, viscous, poorly fermentable fiber improves stool viscosity and symptoms especially patients with IBS-C.

There are also recommendations for new medications. These include Lubiprostone (Amitiza) and Linaclotide (Linzess) for IBS-C, and nonabsorbed antibiotics Rifaximin (Xifaxan) for IBS-D.

Recently, a subset of patients with IBS-D (about 20-30 %) is reported to have bile acid malabsorption (BAM), which contributes to diarrhea. Testing for BAM is the SeHCAT test, which is only available in some European countries. Alternatively, serum fibroblast growth factor 19 (FGF-19) and serum C4 may also help identify BAM. These tests will soon be available in many countries, and if identified, either colestipol or colesevelam would be the treatment of choice.



IBSはローマIV診断基準によって診断されます。すなわち; 過去3か月間に平均して少なくとも1日/週の反復性腹痛があり、次の3つの基準のうちの2つ以上を含むこと。 (1)排便に関連する(2)便の頻度の変化に関連する(3)便の形態の変化に関連する。診断の少なくとも6か月前に症状が現れ、過去3か月間基準を満たす必要があります。膨満感は一般的に報告されている症状ですが、その存在はIBSの診断に必須ではありません。

便が異常であると認識された日の代表的な便形態によって、IBSは4つの異なるサブタイプに分類されます:IBS-D(下痢)、IBS-C(便秘)、IBS-M(混合)、およびIBS -U(有意なパターンなし)。 このサブタイピングは、診断研究と治療法を適切に選択するために重要ですが、IBS患者の半数以上が1年間のうちに優勢なサブタイプが変化します。 現在の薬理学的療法は、下痢と便秘のサブタイプのみを対象としています。

IBSの明確なバイオマーカーがないため、診断は2016年に確立された上記のローマIV診断基準に依存します。American Journal of Gastroenterologyは、科学研究の発展によりいくつかの新しいエビデンスを含むIBSの2021ガイドラインを公開しました。 そのいくつかをここで紹介します。

IBS-Dの患者では、セリアック病を除外するために血清学的検査が推奨されます。 これらの検査には、IgA組織トランスグルタミナーゼと定量的IgAレベルが含まれます。 また、IBS-Dの患者では、糞便中のカルプロテクチンと血清CRPの組み合わせを使用して炎症性腸疾患(IBD)を除外することができます。

発展途上国または水質の悪い地域の患者では、寄生虫感染、特にジアルジアをチェックすることもお勧めします。 テストには、糞便イムノアッセイまたはPCRが含まれます。 細菌性およびウイルス性胃腸炎は急性の炎症症状を伴いますが、寄生虫感染症は、IBSと同様に、無症候性から腹部膨満、下痢、腹痛の慢性症状までさまざまです。 ジアルジアへの曝露は、食物不耐性の発症にも関連しています。

IBSの治療に関しては、現在のところ、低FODMAP(発酵性オリゴ糖、二糖、単糖、およびポリオール)ダイエットや、いかなる菌種を用いたプロバイオティクスの使用を支持するエビデンスは、いくつかの有益な効果があるにせよ、ほとんどありません。 一方、すべてのサブタイプのIBS症状の治療には、可溶性であるが不溶性ではないファイバーが推奨されます。 可溶性ファイバーはオオバコ、オートブラン、大麦、豆に含まれ、不溶性ファイバーは小麦ふすま、全粒穀物、一部の野菜に含まれています。 溶解性、粘性、発酵性の低いファイバーは、特にIBS-Cの患者の便の粘度と症状を改善します。

新しい薬の推奨事項もあります。 これらには、IBS-C用のルビプロストン(Amitiza)とリナクロチド(Linzess)、およびIBS-D用の非吸収性抗生物質リファキシミン(Xifaxan)が含まれます。

最近、IBS-Dの患者のサブセット(約20-30%)が、下痢の一因となる胆汁酸吸収不良(BAM)を持っていると報告されています。 BAMの診断はSeHCATテストであり、ヨーロッパの一部の国でのみ利用できます。 あるいは、血清線維芽細胞成長因子19(FGF-19)および血清C4もBAMの同定に役立つ可能性があります。 これらの検査はまもなく多くの国で利用可能になり、診断された場合は、コレスチポールまたはコレセベラムなどが治療法として選択されるでしょう。

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