Initial Evaluation
When evaluating the constipated patient, it is necessary to be cognizant of the multifaceted
nature of the problem.[9]
[10]
[11]
[12]
[13] Female sex, older age, low fiber diet, a sedentary life style, malnutrition, polypharmacy,
and a lower socioeconomic status have all been identified as risk factors for constipation.[9]
[11]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21] Given the subjective nature of patients’ perceptions of what defines constipation,
the first task is to clarify specific symptoms and severity of constipation. To establish
that, the clinician should ask specific questions rather than rely on the patient
to volunteer the information related to their particular symptoms. It is imperative
to obtain a full and exhaustive medical history to rule out secondary causes of constipation
resulting from medication[22] ([Table 3]) or other etiologies as outlined in [Table 4]. Complaints of prolonged or incomplete defecation, excessive straining, the need
for pelvic support, or digital manipulation are suggestive of pelvic floor dysfunction.
Conversely, feelings of pain, bloating, or colicky pains that are relieved with defecation
suggest a diagnosis of IBS ([Table 2]). It is useful to adopt a scoring system to simplify and objectively gauge the extent
of complaints. The Wexner constipation score incorporates frequency of bowel movements,
difficulty or pain on evacuation, feelings of incomplete evacuation, abdominal pain,
time spent in the lavatory, the use of laxatives or digital assistance, failed evacuation
attempts per 24 hours, and the duration of constipation symptoms. The Wexner score
(minimum score, 0; maximum score, 30) correlates well with objective physiologic findings
found on further testing and provides a baseline in the evaluation of the constipated
patient.[23]
Table 3
Medications Associated with Constipation[6]
Antacids (more common when containing aluminum or calcium)
|
Iron and calcium supplements
|
Opioids and other narcotics
|
Anticholinergic agents
|
Calcium channel blockers
|
Diuretics
|
Nonsteroidal anti-inflammatory drugs
|
Sympathomimetics
|
Tricyclic antidepressants
|
Table 4
Etiology of Chronic Constipation[22]
Mechanical
|
Metabolic
|
Neuropathies
|
Myopathies
|
Cancer
|
Diabetes mellitus
|
Hirschsprung disease
|
Scleroderma
|
Stricture
|
Hypothyroidism
|
Parkinson disease
|
Amyloidosis
|
Rectocele
|
Hyperparathyroidism
|
Injury to nervi erigentes
|
|
Sigmoidocele
|
Hypercalcemia
|
Paraplegia
|
|
Enterocele
|
Hypokalemia
|
Multiple sclerosis
|
|
Abnormal perineal descent
|
Hypomagnesemia
|
|
|
Intussusception
|
Uremia
|
|
|
Rectal prolapse
|
Depression
|
|
|
Paradoxical puborectalis contraction
|
|
|
|
Megacolon
|
|
|
|
Colonic inertia
|
|
|
|
Anal fissure
|
|
|
|
Physical Exam
The office examination should include an abdominal exam, a perineal exam, and a rectal
exam. Due to the sensitive nature of the examinations involved, it is important to
go from least invasive (abdominal exam) to most (rectal exam) to build patient rapport
and prevent anxiety, fear, or muscle guarding, which might affect the evaluation.[24] The abdominal exam should rule out any palpable masses, hepatomegaly, or other reasons
that can be the cause of the patient's presenting symptoms. While the patient is still
supine, both inguinal regions are examined to rule out any hernias before instructing
the patient to assume the left lateral position or prone for the remaining part of
the examination. The perineum is evaluated thoroughly for evidence of external hemorrhoids,
skin tags, anal warts, fissures, or abnormal descent upon pushing (more than 3 cm).
A digital examination is done to evaluate sphincter tone (resting and squeeze) and
to rule out any palpable rectal masses or obvious rectocele. A side-viewing anoscope
is then inserted to rule out any enlarged internal hemorrhoids or any other anal pathology.
After obtaining a full history and completing the physical examination a differential
diagnosis can be established and further testing is tailored on a case by case basis.
In patients older than 30 years old who present to our practice complaining of constipation,
routine blood work to evaluate electrolyte abnormalities and a colonoscopy are recommended.
Types of Functional Constipation
Slow transit and obstructive defecation comprise the two subtypes of functional constipation.
The former being due to diminished motility causes longer transit time through the
colon, whereas obstructive defecation is the inability to propagate the stool out
of the rectum. In all patients complaining of constipation, 11% have slow transit
constipation, 13% have obstructive defecation, and the vast majority has constipation
due to IBS.
Slow Transit Constipation
Slow transit constipation, or colonic inertia, is defined as long transit time through
the colon. Meals, stress, medical conditions, spinal cord lesions, sleep-wake cycle,
endocrine and renal conditions have all been cited in the medical literature as causes
of slow transit constipation.[9]
[25] Symptoms of slow transit constipation reported by patients are vague and include
infrequent urges to defecate, bloating, and abdominal discomfort. In addition, attempts
by the clinician to ameliorate this type of constipation with fiber supplements are
usually not successful.[26] The most common test used to diagnose slow transit constipation is the Sitzmark
transit study. Scintigraphic defecography, which measures colonic motility via radionucleotide
scanning, is much less commonly performed.
Sitzmark Study
First described in the 1969 by Hinton et al, the Sitzmark test is still widely used
today for the workup of functional constipation.[27] Prior to performing a Sitzmark test, the patient is first instructed to abstain
from using laxatives, enemas, or suppositories for 5 days. The patient is then instructed
on day 0 to ingest one gelatin capsule containing 24 precut radiopaque polyvinyl chloride
markers (each of which is 4.5 mm × 1 mm). On day 5, a flat plate of the abdomen is
obtained. Patients who have normal colonic motility will expel over 80% of the markers.
Patients who retain five or more radiopaque markers have a positive study. If the
retained markers are scattered about the colon, the patient most likely has colonic
inertia. However, an accumulation of markers in the rectosigmoid most likely points
to an etiology of functional outlet obstruction. Metcalf et al developed a protocol
for the Sitzmark test that uses three different types of radiopaque markers (O markers,
Double-D markers on day 1, and Tri-Chamber markers on day 2). A flat plate is taken
on day 4 and again on day 7 if necessary. Metcalf's protocol with different radiopaque
markers on different days is more complicated to interpret, however, it is more useful
in diagnosing segmental areas of colonic inertia.
A number of variations of the test have been described. One method involves the patient
ingesting the capsule on Sunday night and obtaining abdominal x-rays on Monday, Wednesday,
and Friday morning (days 1, 3, 5). The presence of markers in the colon on the initial
Monday morning x-ray excludes a gastric or small bowel motility problem. The subsequent
two films provide a general pattern of marker movement.
Nuclear Scintigraphic Defecography
Radionucleotide scintigraphy is a noninvasive nuclear medicine test that provides
regional as well as overall colonic transit motility information. The radionuclide
111-diethylenetriamine pentaacetic acid (111In-DTPA) is used in this colonic transit study. When it was first introduced, scintigraphic
defecography required introduction of 111In-DTPA to the cecum antegrade by placing a tube orally to intubate the cecum or retrograde
via a tube placed during colonoscopy. The invasive nature of both of those studies
has led researchers at the Mayo Clinic to develop a resin-coated capsule that releases
its contents in the distal ileum's pH of 7.4. The patient is placed under a gamma
probe and colonic motility is analyzed by scintigraphic scans of the patient again
at 24 hours and 48 hours. A quoted benefit of scintigraphy is the ability to also
combine technetium-99 (Tc99) with 111In-DTPA to obtain motility studies of the stomach and small bowl in addition to the
colon (whole gut transit scintigraphy). This comprehensive study helps rule out diffuse
gastrointestinal dysmotility as a cause of the patient's slow transit constipation.
Moreover, one has to be aware of the low percentage (20%) of slow transit cases that
are also associated with obstructive defecation.
Obstructive Defecation
Causes of obstructive defecation syndrome (ODS) can be multifactorial ranging from
mechanical, physiologic, to congenital. ODS largely affects the female population,
and is characterized by difficulty evacuating requiring use of mechanical aids, digitation,
excessive straining, incomplete evacuation, and excessive time needed to evacuate.
ODS has been linked to anatomic abnormalities of rectocele, rectoanal or rectorectal
intussusception, paradoxical puborectalis contraction, pelvic organ prolapse, descending
perineum syndrome, solitary rectal ulcer syndrome, sigmoidoceles, and enteroceles.[27] However, abnormal findings on anorectal studies such as rectoceles may be seen in
asymptomatic subjects. Functional abnormalities such as pelvic floor dyssynergia,
decreased rectal compliance, and decreased rectal sensation have also been shown to
contribute to symptoms of ODS. Although the symptomatology has been well defined in
the literature, the pathophysiology and etiology of this syndrome are still poorly
understood.[28]
Anorectal physiologic studies to evaluate the patient with obstructive defecation
include electromyography, anorectal manometry, rectal anal inhibitory reflex (RAIR),
balloon expulsion test, and paradoxical puborectalis contraction. Radiologic studies
include triple contrast defecography under fluoroscopy and dynamic magnetic resonance
imaging (MRI) defecography, which are used to evaluate anatomic and functional causes
of ODS.
Electromyography
Pelvic floor electromyography (EMG) analyzes the motor unit action potentials (MUAP)
of the pelvic floor musculature.[29] EMG tracings outline the duration, amplitude, and recruitment during voluntary squeeze
and push maneuvers providing helpful information to complement other anorectal tests
performed. EMG can be performed using skin electrodes (surface noninvasive EMG), an
anal plug, or a concentric needle (invasive EMG). The surface EMG method has been
shown to be equivalent to the concentric needle technique[30] and carries a good negative predictive value (91%) to rule out paradoxical puborectalis
contraction (PPC). Owing to its simplicity and dependability, surface EMG is the test
of choice in our practice. PPC can be diagnosed on EMG when MUAP recordings from the
puborectalis fail to decrease during attempted evacuation. However the positive predictive
value is low with EMG (31%) and an EMG test suggestive of PPC should trigger further
definitive testing with cinedefecography.[31] EMG-equipped anal plugs are commonly used during biofeedback sessions for pelvic
floor muscle retraining in patients with functional outlet obstruction (i.e., paradoxical
puborectalis contraction).[29]
Anorectal Manometry
Manometry remains the most widely used anorectal physiology investigative tool. Several
different anorectal physiology recording systems are available. Catheters and pressure
transducers used in manometry are thin and flexible. Anorectal manometry catheters
range from solid-state probes to water perfused or air charged. Anorectal manometry
can evaluate sphincter pressure while the patient is resting, squeezing, and attempting
to defecate. With the patient in the left lateral decubitus position or lithotomy,
the manometry catheter is introduced into the rectum and pulled back through the anal
canal with measurements taken at intervals to determine the rest, squeeze, and push
pressures of the anal sphincter. Normal ranges differ by age and gender and patients
should be compared to matched normal individuals.[32]
[33] As a general rule, all manometric amplitudes decrease with age.[34]
In addition to direct sphincter pressure measurements, the presence or absence of
rectoanal reflexes and rectal sensory function can be assessed easily. Distention
of the rectum by feces can be simulated by inflating a rectal balloon with air while
monitoring anal sphincter pressures.[35] In normal individuals, with sudden distention of the rectum—as with the arrival
of a bolus of feces—the internal anal sphincter relaxes. The amount of inhibition
of the anal sphincter and the duration of relaxation both seem to be proportional
to the amount of rectal distension.[36] If a clinician is unable to illicit a RAIR with the initial attempt, a larger volume
of air should be used to distend the rectum before registering the RAIR as missing.
RAIR is present even in patients with high spinal cord lesions.[37]
Balloon Expulsion Test
First described by Barnes,[38] the balloon expulsion test is another tool available to assess rectoanal coordination
during defecation. Many variations have been described when performing this test.[39] Some recent studies support individualizing the amount of volume instilled into
the balloon depending on tested sensation thresholds obtained prior to performing
the expulsion test. Normal subjects can increase their intraabdominal pressure above
80 mmHg and successfully expel the balloon in a median of 50 seconds.[40] The inability of a subject to expel the balloon is suggestive of an outlet obstruction
and should trigger further anorectal testing (i.e., cinedefecography).[41]
[42]
Paradoxical Puborectalis Contraction
During normal defecation, the pelvic floor relaxes to increase the anorectal angle.
As the anorectal angle becomes more obtuse, the evacuation of stool is facilitated
through the relaxed anal sphincter. Failure of the puborectalis muscle to relax or
paradoxical contraction results in obstructed defecation.[43] In patients reporting excessive straining, prolonged periods of defecation, feelings
of incomplete evacuation, and a need for digitations, PPC may be the cause of pelvic
floor dysfunction.[44] Patients suffering from PPC may have an underlying psychological component and may
benefit from biofeedback sessions aimed at training them to relax their pelvic floor
during defecation. In the long term, biofeedback often loses efficacy and may need
to be repeated.
Cine-Defecography
Cine-defecography is a radiologic evaluation that provides insight into anorectal
structure and function. Initial fluoroscopic studies of defecation date back to 1952
when Lennart Wallden investigated causes of obstructed defecation.[44] Defecography studies are indicated in patients when an outlet anatomic or functional
disorder is suspected as the cause of constipation.[45]
[46]
[47]
Triple-contrast defecography requires oral, vaginal, and rectal opacification. The
patient is instructed to consume a barium meal 1.5 hours before the examination. In
women, vaginal opacification is recommended to enhance the contrast imagery. Thirty
minutes prior to performing cinedefecography, the patient's rectum is cleared with
a sodium phosphate enema (Fleet™; C.B. Fleet Co., Lynchburg, VA). The test should
be explained in detail to patients to obtain their full cooperation. First, the patient
is placed in the left lateral decubitus (Sims) position and a 50-mL barium enema followed
by air insufflation is administered to delineate the rectal mucosa. Second, the rectum
is opacified with a barium paste product (Anatrast®; E-Z-EM, Westbury, NY) that resembles stool in weight and consistency. A caulking
gun injector is used to fill the rectum with 250 cc (500 g)—less if the patient reports
fullness—of thick barium paste. As the caulking gun is withdrawn from the rectum,
barium paste is also injected into the anal canal. The patient is then seated on a
water-filled radiolucent commode (Sunburst, Ladson, SC). Lateral films are first taken
to localize the bony landmarks and to check the quality of the various contrast agents
given. Fluoroscopic images are obtained at rest, during squeezing, and while the patient
is defecating. Maintaining patient privacy during defecation is very important. This
can be achieved by keeping the radiology suite as quiet as possible, and by positioning
the patient out of the view of the technologists during defecation.
Despite many improvements to standardize this study,[48]
[49]
[50]
[51] differences still exist in the way measurements are taken by individual examiners.[52]
[53] The anorectal angle (ARA) is the angle between the axis of the anal canal and the
distal half of the posterior wall of the rectum. When a patient squeezes, the anorectal
angle becomes more acute preventing defecation. Relaxing the puborectalis muscle causes
the anorectal angle to increase and become more obtuse and elevating the intraabdominal
pressure allows defecation to occur. Pathologic findings on defecography are abnormal
perineal descent, non-emptying rectocele, rectal prolapse, PPC, enterocele, and sigmoidocele.
Fluoroscopic x-ray defecography subjects the patient to a mean radiation dose of 4.9
mSv, most of which is concentrated in the pelvis making it contraindicated in pregnancy.[54]
[55]
[56]
Dynamic MRI Defecography
MRI defecography made its debut with the advent of open-configuration MRI, which made
it possible to image patients in the vertical position.[57] MRI defecography overcomes the projectional limitations of fluoroscopic defecography
and can be safely used in patients when pelvic radiation is contraindicated (i.e.,
pregnancy). In addition, MRI defecography depicts perirectal soft tissue and can detect
more clearly pelvic floor descent, rectoceles, and intussusceptions.[58] A wide variety of techniques is present in the literature on the best method to
perform this test. For example, patients may be positioned in the supine or sitting
position; ultrasound gel or mashed potatoes loaded with gadopentetate dimeglumine
may be used for rectal contrast.[59] Proponents of MRI prefer its better interobserver consistency and quality images
that delineate bony structures from surrounding soft tissue.[60] However, the lower temporal resolution and higher cost of an MRI contrasted exam
have hindered MRI defecography from widespread use; a lot of valuable information
may be obtained via the cheaper and simpler fluoroscopic defecography.
Anatomic Abnormalities
Rectoceles, sigmoidoceles, enteroceles, rectoanal intussusception, and rectal prolapse
are all anatomic abnormalities that can be detected on fluoroscopic or MRI defecography.
The most common finding on defecography is a rectocele. A rectocele is a protrusion
of the anterior rectal wall beyond its normal anatomic position (usually towards the
vagina) and can be present in up to 80% of normal subjects.[61] Rectoceles over 2 cm are significant and usually alter the direction of the propulsive
forces into the rectocele itself rather than towards the anus, thus obstructing defecation.[59] In a recent study, 39% of women over 50 had a significant rectocele diagnosed on
defecography and 75% of women over 50 with a prior vaginal delivery have evidence
of concomitant intussusception and rectocele.[62] Obstetric trauma during vaginal delivery and pelvic relaxation have both been cited
as causative agents leading to the development of abnormalities on defecography studies
done in women. Standard terminology classifies rectoceles in women as low, midvaginal,
or high.[63] Hysterectomy, postmenopausal status, anismus, dyssynergic defecation, and chronic
constipation have all been associated with rectocele.[64] Most of the physiologic findings are unchanged in patients with an isolated finding
of a rectocele. Sigmoidoceles, enteroceles, and rectoanal intussusception are all
anatomic variants found in normal patients, extremes of which can lead to obstructive
defecation and mandate surgical intervention for repair.