Availability of Full-Thickness Tissue

It is evident that diagnoses that depend on histologic examination of nerve, muscle, and ICC cannot be made using standard endoscopic biopsies. Thus in the main, tissues studied must be derived from full-thickness, or near full-thickness, biopsies taken with deliberate diagnostic intent or alternatively as the byproduct of emergency or planned surgical interventions. On this basis, tissues may take the form of deep seromuscular or full-thickness biopsies or resection specimens. The role of suction rectal biopsies in the management of Hirschsprung disease (HSCR) is well established and is not discussed further here. Regrettably, there are few other well documented instances in which biopsy diagnoses clearly alter clinical care. Thus, although there are times that a bowel segment is discarded at the time of surgery and can be legitimately processed without additional risk to the patient, incidental biopsy at the time of other surgeries or as a planned procedure is more difficult to justify. Nevertheless, there is increasing evidence and agreement that minimally invasive (laparoscopic) biopsy techniques add little risk, which may be acceptable, in the context of improving the situation for the patient with severe symptoms in whom structural lesions detectable using radiologic and endoscopic techniques are absent. There is, however, no certainty that structural evidence of disease should be sought using full-thickness biopsy in all patients with otherwise unexplained abnormalities of gastrointestinal (GI) motor activity. Further, limitation on number (usually one) and size of biopsy inevitably leads to the possibility of sampling error in patchy diseases such as focal plexitis or leiomyositis.

Standardization of Preparative and Staining Methods

The main aim of the first IWG guideline, published in 2009, was to evaluate the literature and bring together expert opinion to set acceptable standards of practice for the general pathologist in regard to procurement and preparation of tissue for study, methods of sectioning, and evaluation by routine and other techniques. The IWG noted that extraordinary variability existed in histopathologic techniques used for the study of tissues from patients with suspected GI neuromuscular pathology with wide differences in methodologies and expertise continuing to confound the significance and reliability of a variety of reported histopathologic changes in terms of clear delineation from normality. This was highlighted by a prior survey of practice in which 86 out of 130 European and U.S. histopathology laboratories processed tissue for suspected GI neuromuscular pathology, but only 33 performed more than a single hematoxylin and eosin (H&E) section. Of those that did more specialized tests, none did exactly the same tests. Methodological issues are discussed for specific histopathologic findings in the text that follows.

Limitations on Availability of More Complex Methods

The IWG was cognizant of the problems faced by general pathologists who receive specimens very infrequently and who may not have resources at their disposal to perform methods that require inordinate effort or specialized equipment. Thus, many techniques employed in the research literature are not relevant to challenges in everyday practice. These include the use of thick sections, multiple immunolabeling, and fluorescence and confocal microscopic or ultrastructural techniques. The IWG collated several referral recommendations for equivocal diagnoses that might benefit from further, more complex, studies at an index or specialist laboratory. Where results from these techniques may become relevant to future practice they have been included in this review but indicated as such.

Standardization of Preparative and Staining Methods

The main aim of the first IWG guideline, published in 2009, was to evaluate the literature and bring together expert opinion to set acceptable standards of practice for the general pathologist in regard to procurement and preparation of tissue for study, methods of sectioning, and evaluation by routine and other techniques. The IWG noted that extraordinary variability existed in histopathologic techniques used for the study of tissues from patients with suspected GI neuromuscular pathology with wide differences in methodologies and expertise continuing to confound the significance and reliability of a variety of reported histopathologic changes in terms of clear delineation from normality. This was highlighted by a prior survey of practice in which 86 out of 130 European and U.S. histopathology laboratories processed tissue for suspected GI neuromuscular pathology, but only 33 performed more than a single hematoxylin and eosin (H&E) section. Of those that did more specialized tests, none did exactly the same tests. Methodological issues are discussed for specific histopathologic findings in the text that follows.

Limitations on Availability of More Complex Methods

The IWG was cognizant of the problems faced by general pathologists who receive specimens very infrequently and who may not have resources at their disposal to perform methods that require inordinate effort or specialized equipment. Thus, many techniques employed in the research literature are not relevant to challenges in everyday practice. These include the use of thick sections, multiple immunolabeling, and fluorescence and confocal microscopic or ultrastructural techniques. The IWG collated several referral recommendations for equivocal diagnoses that might benefit from further, more complex, studies at an index or specialist laboratory. Where results from these techniques may become relevant to future practice they have been included in this review but indicated as such.

Availability of Normative Human Data

The definition of disease (see the section that follows) is dependent on a clear concept of what constitutes normality, which is a particular problem when diagnoses depend on subtle qualitative or quantitative findings. This is exemplified by neuropathy or loss of ganglion cells wherein lack of adequate control data for elements of the human enteric nervous system (neuronal cell bodies, glial cells, and nerve fibres) led the IWG to systematically review 40 studies using techniques that could be deemed applicable to the practicing pathologist. The results revealed a disappointing lack of concordance between observations of different investigators, resulting in data insufficient to produce robust normal ranges. This diversity further affirms the need to standardize the way pathologists collect, process, and quantitate neuronal and glial elements and to make a diagnosis only within the limits of confidence in the sample size. For instance, in the only available controlled study analyzing myenteric neuron counts in the whole circumference of the infant rectum, reliable estimates of the actual neuronal density required at least five full- ci rcumference sections.

Clear Definition of Abnormality (in the Individual)

The diagnosis of disease in an individual is very different from establishing that significant differences exist in a particular quantitative finding between groups of patients and controls. The latter gives valuable information on the possible biology of disease but does not necessarily help define the cutoff for diagnosis for the pathologist facing a histologic section. This problem does not occur in categorical decisions based on binary qualitative observations, for example, neurons present or absent, muscle vacuolation and fibrosis present or absent. Unfortunately, such diagnoses are limited, in the most part, to infantile phenotypes of which most, for example, HSCR and hollow visceral myopathy, are rare or readily suspected on clinical/radiologic grounds. The situation is quite different in the more common diagnostic conundrum—that of the adult with chronic disordered motility and pain. Here, many patients have subtle neuropathic findings and the situation is akin to that of small-bowel manometry, in which several studies attest to quantitative abnormalities of the migrating motor complex between patient and control cohorts but normal ranges are so wide that a firm diagnosis in an individual based on whether they fall within or without the normal range is still very difficult. Diagnoses with established definitions that met consensus are listed in Table 1 ; diagnostic criteria for these are shown in Table 2 .

Understanding the Relationship of Abnormality to Observed Clinical Phenotype

Having decided that an adequately prepared and stained representative histopathologic section is abnormal, it is quite a different question as to whether the “validated” histopathologic diagnosis has a specific or causal relationship with the clinical indication for biopsy. A second consensus process was undertaken by the IWG to address this issue with development of a matrix between defined histopathologic phenotypes (from the London Classification) and recognized clinical entities using the development of two “diagnostic grades” ( etiologic or morphologic associated) to indicate strength of relationship. Whereas criteria for making any association were the retrieval of two peer-reviewed publications from different institutions, the decision between etiologic and morphologic was decided by consensus, which was inevitably influenced by several factors:

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  The number, consistency, and quality of reports (weight of publications)

  
  
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  Sensitivity of the finding within these reports, that is, what proportion of patients with a clinical entity had the histologic feature

  
  
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  Specificity of the finding to a single clinical entity (rather than to many clinical syndromes)

  
  
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  Supportive basic science, particularly comparative animal models.

Impact on Patient Management or Prognosis

Aside from the diagnosis of HSCR, there are few other well documented instances in which biopsy diagnoses definitely alter clinical care. Thus the number of patients for which specific therapy can be guided by histopathology is currently limited, for example, using immunosuppressants in diseases characterized by an underlying inflammatory phenotype. Nevertheless, a histopathologic diagnosis can provide valuable insight into the etiology or pathogenesis of some forms of GI neuromuscular disorder (GINMD), which may afford important prognostic value, affect genetic counseling, and direct and prevent additional procedures. One of the other important functions of histopathologic studies in clinical management is the exclusion of particular phenotypes such as overt myopathy or associated phenotypes such as amyloidosis. The IWG defined reporting recommendations to provide for instances in which a “critical” diagnosis might acutely affect management.

Clinical Scope

A complete review of all clinical entities associated with GI neuromuscular pathology is not possible in this article. Diseases in which dysmotility is not the central clinical characteristic (eg, Crohn’s disease; radiation enteropathy; and tumors of nerve, smooth muscle, and ICC) have thus been excluded. Further, other local or systemic conditions with sequelae that include neuromuscular dysfunction, but in which the diagnostic utility of histopathology is questionable, have also been excluded, for example, acute conditions such as postoperative ileus and acute colonic pseudo-obstruction; disease entities with established macroscopic findings, for example, infantile hypertrophic pyloric stenosis, atresias, anorectal malformations, and megacystis–microcolon–hypoperistalsis syndrome; and other systemic diseases leading to sensorimotor dysfunction such as idiopathic autonomic neuropathy, Chagas’ disease, human immunodeficiency virus (HIV), and amyloid-associated neuropathy in which intestinal full-thickness biopsies are rarely undertaken if the primary cause is known. Finally, because it has a specific and sizeable literature elsewhere, HSCR (although undoubtedly one of the more common and important enteric neuromuscular disorders) has also been excluded from this review. Digestive motility disorders have been defined throughout on a physiologic measurement basis in accord with the Bangkok classification with a focus almost exclusively on “well defined entities.” Both primary and secondary motility disturbances are addressed.