Table 3.

Possible advanced diagnostic approaches.

Diagnostic Tool	Description	Diagnosis	Comments
Magnetic Resonance (MR), Computed Tomography (CT), Endoscopy	MR and CT are imaging studies, while colonoscopy is endoscopic examination. All three examinations are used to identify different pathologies in gastrointestinal tract.	Characterization of the specific etiologies and complications of constipation is facilitated by both anatomic and functional imaging which range from basic radiography to MR imaging and endoscopy.	Procedures including colonoscopy, MR and CT can be very effective in obtaining evidence for the cause of unexplained symptoms, the use of chronic laxative and possible mucosal lesions. However, patients during CT are exposed to ionizing radiation.
Balloon Expulsion Test (BET)	Measures time required for a patient in a seated position to evacuate a balloon filled with water or air; instead of balloons artificial stool may be used [39,40].	Normal expulsion time varies from 1 min to 5 min, however sensitivity and specificity is higher for 2 min cut-off in constipation. Longer time is characteristic for patients suffering from dyssynergic defecation.	Even though, the test is highly sensitive and specific for defecatory disorders, the results might be falsely negative in some patients, for example with pelvic laxity (rectocele, sigmoidocele etc.) [23,39]. Other patients may strain overly and eject the balloon and the result does not express normal functions of their anus and rectum.
Anorectal manometry (AM)	Assesses anal and rectal pressure during attempted defecation and at rest. AM also measures rectal sensation, compliance and rectoanal reflexes [41].	2 out of 5 abnormalities should be present during manometry to recognize defecation disorders: Anal pressure during defecation > 90th percentile Anal pressure in rest > 90th percentile Anal relaxation < 10th percentile Rectal pressure < 10th percentile Rectoanal gradient < 10th percentile [23]	AM is mostly suggested to diagnose dyssynergic defecation, it is especially dedicated to confirm Hirschsprung disease. When a patient attempts to defecate normally, pressure in rectum rises. This increase is synchronized with a decrease in anal sphincter pressure, mainly because of relaxation of the external anal sphincter. This maneuver is voluntary. The inability to achieve this coordination is mostly observed in patients with dyssynergic defecation. Conventional AM collects data from single points, whereas high-resolution AM collects circumferential data, from the whole anal canal and distal part of the rectum. To reduce artificial movements and to improve spatial resolution of anorectal pressures, high-resolution AM catheters are used [42]
Rectal Sensation Testing (RST)	Simple test with the use of balloon that is attached to a catheter, and the balloon in the rectum is filled with air. Patient reports first sensations, desire to evacuate, urgency and maximum of their tolerance [34].	Reduced sensitivity of the rectum to distention indicates hyposensitivity (e.g., in constipation predominant subtype of irritable bowel syndrome (IBS-C) or spinal cords injuries), whereas increased sensation indicates hypersensitivity (e.g., fecal urgency, diarrhea predominant IBS, ulcerative colitis).	Results may be affected by biomechanic or structural properties of the rectum.
Defecography	Contrast material (150 mL) in rectum allows to investigate anorectal region during defecation and at rest [3,4].	Usually performed in case of a discrepancy between clinical impression and AM, or when structural abnormalities are assumed [7]. The test may reveal long time of retention of contrast material, decreased activation of levator muscles, absence of a stripping wave in the rectum or inability in expulsion of the barium.	The drawback of this examination is radiation exposure, patient embarrassment, inconsistent methodology, and limited availability. Due to these disadvantages defecography is not performed routinely [3,4].
Colonic Transit Study (CTS)	There are 3 methods of assessment stool transit: Colonic transit scintigraphy. Abdominal radiography of the ingestion of radiopaque marker. Tracking of the movement of the ingested wireless motility capsule [4].	Scintigraphy: Colonic transit is evaluated on the basis of the geometric center (GC). GC is the weighted average of the isotope distribution within the colon and stool. Patients with GC at 24 h less than 1.7, and GC at 48 h less than 3.0 are considered to have slow transit. Radiography: Decreased transit time is defined as presence on an abdominal X-ray of more than 5 markers in the colon after 5 days after capsule ingestion [3]. Wireless motility capsule: Slow transit is diagnosed above the 95th percentile of the normal subjects, what is identified as 59 h [43].	By reason of high costs, safety and availability, abdominal radiography of the ingestion of radiopaque marker is the preferred method. A CTS cannot differentiate between patients with slow-transit constipation and isolated dyssynergic defecation [3].
Fecobionics	An artificial stool which collects dynamic measurements of multiple variables in the process of defecation in a single examination. This technology provides integrated measurements of bending angle, pressure and geometric profiles with assessment of sensation [44].	Possible application in diagnosis of chronic constipation and fecal incontinence and in dyssynergic defecation in biofeedback training [45].	Fecobionics is still a research technology, however it has a vast potential.
Neurophysiology testing and electromyography	Records the activity of the muscle of the anal sphincter [34].	Diagnosing neuronal innervation and providing information about neuromuscular function. Abnormal activity may be an evidence for denervation, which is present in injury of the pudendal nerve or cauda equina syndrome.	Both tests are rarely used, because of limited availability. Moreover, they are troublesome and painful examination, thus it is performed only in a few research centres.