Constipation is the passage of infrequent or hard stools
with straining. “Infrequent” is defined as < 3 times/week, and “hard” is
defined as stools with water content < 50ml. As mentioned previously, it is
a very common condition, increasing in prevalence with age and affecting more
females than males. Having said that, constipation is less common in Africa and
India, where stool weight is 3~4 times greater than Western countries.
Constipation can have many different causes. The most common
one is idiopathic, attributed to colon dysmotility—but this is very difficult
to quantify. Other organic causes include medication side effects (narcotics,
antidepressants), intestinal obstruction, left sided colon cancer (consider in
older populations), and fecal impaction. Metabolic causes such as diabetes
mellitus, hypothyroidism, hypercalcemia, hypokalemia, and uremia can also
result in constipation, as do neurological causes such as intestinal
pseudo-obstruction, Parkinson’s disease, and multiple sclerosis. Some collagen
vascular diseases (e.g. scleroderma) can cause constipation; and painful anal
conditions (e.g. fissures) can definitely cause constipation too.
Mnemonic for causes of constipation: DOPED
Drugs
Obstruction
Pain
Endocrine dysfunction
Depression
Clinical presentation of constipation can be very similar to
that of IBS. The stool is firm, difficult to expel, and passed with straining.
There is associated abdominal pain that is relieved by flatulence and
defecation. Other symptoms include tenesmus, abdominal distention, overflow
diarrhea, and infrequent bowel movements.
If constipation is the only symptoms, the underlying disease
can be very difficult to find; the only test recommended by American
Gastroenterology Association (2013) would be CBC—to exclude any sinister,
systemic conditions. However, TSH, calcium, and glucose levels can also be
helpful, as is an abdominal X-ray. If the constipation is associated with
rectal bleeding, weight loss, or anemia, visualization of the colon through
colonoscopy or CT colonography would be indicated.
For constipation that is refractory to treatment, colon
transit time can be measured by having the patient ingest radio-opaque markers
then taking a series of abdominal X-rays. The normal time is around 70 hours.
If the colon transit time test result is indeed normal, then the patient has a
misperception of normal defecation (IBS). If the result is prolonged
throughout, the patient has “colonic inertia” (infrequent bowel movements with
gas/bloating, often occurring in youth). If the result shows outlet
obstruction, it could be that the patient is unable to coordinate pelvic muscles
to empty rectum, causing straining. This tends to occur in old age, and often
stool will be found in rectum on digital exam.
Treatment (in order of increasing potency):
·
Dietary fiber
o Useful
in mild/moderate constipation
o Aim
for 30g daily, increasing dosage slowly
·
Surface-acting agents (to soften and lubricate
stools)
o Docusate
salts
o Mineral
oils
·
Osmotic agents (effective in 2~3 days)
o Lactulose
o Sorbitol
o Magnesium
salts
o Lactitol
o Polyethylene
glycol 3350
·
Cathartics/stimulants (effective in 24 hours)
o Castor
oil
o Senna
(avoid prolonged use to prevent melanosis coli)
o Bisacodyl
·
Enemas and suppositories
o Saline
o Phosphate
o Glycerin
o Bisacodyl
·
Prokinetic agents
o Prucalopride
·
Linaclotide—increases water secretion into the
intestinal lumen.
