Secretory diarrhoea with high faecal potassium concentrations: a new mechanism of diarrhoea associated with colonic pseudo-obstruction? Report of five patients. ACTA ACUST UNITED AC. 2008;32:401-404. [PMID: 18394839 DOI: 10.1016/j.gcb.2007.11.014]

Congenital Diarrheal Syndromes

Congenital diarrheal disorders are heterogeneous conditions characterized by diarrhea with onset in the first years of life. They range from simple temporary conditions, such as cow's milk protein intolerance to irreversible complications, such as microvillous inclusion disease with significant morbidity and mortality. Advances in genomic medicine have improved our understanding of these disorders, leading to an ever-increasing list of identified causative genes. The diagnostic approach to these conditions consists of establishing the presence of diarrhea by detailed review of the history, followed by characterizing the composition of the diarrhea, the response to fasting, and with further specialized testing.

Secretory diarrhea and hypokalemia associated with colonic pseudo-obstruction: A case study and systematic analysis of the literature

BACKGROUND

Colonic pseudo-obstruction (CPO) is characterized by colonic distention in the absence of mechanical obstruction or toxic megacolon. Concomitant secretory diarrhea (SD) with hypokalemia (SD-CPO) due to gastrointestinal (GI) loss requires further characterization.

AIM

To perform a systematic review of SD-CPO, report a case study, and compare SD-CPO with classical CPO (C-CPO).

METHODS

We performed a search of MEDLINE, EMBASE, Cochrane, and Scopus for reports based on a priori criteria for CPO, SD and GI loss of potassium. An additional case at Mayo Clinic was included.

RESULTS

Nine publications met inclusion criteria, with a total of 14 cases. Six studies had high, three moderate, and our case high methodological quality. Median age was 74 years (66-97), with 2:1 male/female ratio. Kidney disease was present in 6/14 patients. Diarrhea was described as profuse, watery, or viscous in 10 patients. Median serum, stool, and urine potassium concentrations (mmol/L) were 2.4 (range: 1.9-3.1), 137 (100-180), and 17 (8-40), respectively. Maximal diameter of colon and cecum (median) were 10.2 cm and 10.5 cm, respectively. Conservative therapy alone was effective in five out of 14 patients. Median potassium supplementation was 124 mEq/d (40-300). Colonic decompression was effective in three out of six patients; one had a total colectomy; three out of 14 had died. The main differences between SD-CPO and C-CPO were lower responses to treatments: conservative measures (35.7% vs 73.6%, P=.01), neostigmine (17% vs 89.2%, P<.001), and colonic decompression (50% vs 82.4%, P=.02).

CONCLUSION

SD-CPO is a rare phenotype associated with increased fecal potassium and is more difficult to treat than C-CPO.

Hypokalemia Associated with Colonic Pseudo-Obstruction (Ogilvie's Syndrome)

We report a case of hypokalemia resulting from colonic pseudo-obstruction or Ogilvie's syndrome. Colonic pseudo-obstruction is characterized by profuse watery diarrhea that has a low sodium and high potassium concentration. It is seen in a variety of medical and surgical conditions, but its exact cause remains unknown. It is thought to result from an imbalance of sympathetic and parasympathetic input in the distal colon. The diarrhea is secretory and driven by potassium secretion rather than the inhibition of sodium reabsorption or chloride secretion, which are the most common pathophysiologic mechanisms of secretory diarrhea. Affected patients often lose >100 mmol of potassium daily. Colonic pseudo-obstruction is associated with a dramatic upregulation of the maxiK or BK potassium channel. This channel plays a prominent role in flow-mediated potassium secretion in the connecting tubule and collecting duct and is also upregulated in the distal colon in patients with advanced chronic kidney disease and end-stage renal disease. In vitro studies show that the channel is regulated by catecholamine binding to the β receptor and cyclic AMP upregulation, somatostatin and aldosterone, insights that can be used to help guide pharmacologic therapy. Nephrologists should be aware of colonic pseudo-obstruction as a cause of extrarenal potassium loss.

The practical value of comprehensive stool analysis in detecting the cause of idiopathic chronic diarrhea

The practical diagnostic value of fecal analysis in the evaluation of patients with chronic nonbloody diarrhea is controversial. It is possible that variations in its value depend on how it is done and how the results are interpreted rather than on its intrinsic value. In the authors' city, stool analysis has been made easily accessible, with a commitment to quality assurance and interpretation. To evaluate its practical value, the results of stool analysis obtained on stool specimens submitted by gastroenterologists were retrospectively reviewed. The results indicate that stool analysis has substantial practical diagnostic value in patients with chronic diarrhea.

Progress in understanding the relationship between diarrhea and intestinal ion transport

Diarrhea is a major cause of morbidity and mortality in the world. There are millions of people dying of diarrhea, and most of them are children. Diarrhea can be divided into acute diarrhea and chronic diarrhea based on the length of the course, and into infectious diarrhea and noninfectious diarrhea according to the etiology. Diarrhea is an imbalance in absorption and secretion of water and electrolytes in the intestine, which involves abnormal ion transport. This paper reviews recent advances in understanding the causes of diarrhea, the relationship between intestinal ion transport and diarrhea, and ion transport in different kinds of diarrhea, with an aim to providing a reference and some new ideas on the comprehensive understanding of the pathogenesis, pathophysiology and treatment of diarrhea.

Activation of the basolateral membrane Cl- conductance essential for electrogenic K+ secretion suppresses electrogenic Cl- secretion

Adrenaline activates transient Cl(-) secretion and sustained K(+) secretion across isolated distal colonic mucosa of guinea-pigs. The Ca(2+)-activated Cl(-) channel inhibitor CaCCinh-A01 (30 μm) significantly reduced electrogenic K(+) secretion, detected as short-circuit current (I(sc)). This inhibition supported the cell model for K(+) secretion in which basolateral membrane Cl(-) channels provide an exit pathway for Cl(-) entering the cell via Na(+)-K(+)-2Cl(-) cotransporters. CaCCinh-A01 inhibited both I(sc) and transepithelial conductance in a concentration-dependent manner (IC(50) = 6.3 μm). Another Cl(-) channel inhibitor, GlyH-101, also reduced sustained adrenaline-activated I(sc) (IC(50) = 9.4 μm). Adrenaline activated whole-cell Cl(-) current in isolated intact colonic crypts, confirmed by ion substitution. This adrenaline-activated whole-cell Cl(-) current was also inhibited by CaCCinh-A01 or GlyH-101. In contrast to K(+) secretion, CaCCinh-A01 augmented the electrogenic Cl(-) secretion activated by adrenaline as well as that activated by prostaglandin E(2). Synergistic Cl(-) secretion activated by cholinergic/prostaglandin E(2) stimulation was insensitive to CaCCinh-A01. Colonic expression of the Ca(2+)-activated Cl(-) channel protein Tmem16A was supported by RT-PCR detection of Tmem16A mRNA, by immunoblot with a Tmem16A antibody, and by detection of immunofluorescence in lateral membranes of epithelial cells. Alternative splices of Tmem16A were detected for exons that are involved in channel activation. Inhibition of K(+) secretion and augmentation of Cl(-) secretion by CaCCinh-A01 support a common colonic cell model for these two ion secretory processes, such that activation of basolateral membrane Cl(-) channels contributes to the production of electrogenic K(+) secretion and limits the rate of Cl(-) secretion. Maximal physiological Cl(-) secretion occurs only for synergistic activation mechanisms that close these basolateral membrane Cl(-) channels.

beta-Adrenergic activation of electrogenic K+ and Cl- secretion in guinea pig distal colonic epithelium proceeds via separate cAMP signaling pathways

Adrenergic stimulation of isolated guinea pig distal colonic mucosa produced transient Cl(-) and sustained K(+) secretion. Transient short-circuit current (I(sc)) depended on beta(2)-adrenergic receptors (beta(2)-AdrR), and sustained I(sc) relies on a beta(1)-AdrR/beta(2)-AdrR complex. Epinephrine (epi) increased cAMP content with a biphasic time course similar to changes in epi-activated I(sc) ((epi)I(sc)). Inhibition of transmembrane adenylyl cyclases (tmACs) reduced peak (epi)I(sc) and cAMP to near zero without decreasing sustained (epi)I(sc), consistent with cAMP from tmAC signaling for only Cl(-) secretion. Inhibition of soluble adenylyl cyclase (sAC) reduced sustained (epi)I(sc) and cAMP to near zero without decreasing peak (epi)I(sc) or cAMP, consistent with cAMP from sAC signaling for K(+) secretion. Sensitivity to phosphodiesterase (PDE) inhibitors and peptide YY (PYY) stimulation further supported separate signaling for the two components. PDE3 or PDE4 inhibitors enhanced peak (epi)I(sc) but not sustained (epi)I(sc), consistent with these PDEs as part of the beta(2)-AdrR signaling domain. PYY suppressed peak (epi)I(sc) in a pertussis toxin (PTx)-sensitive manner, supporting Galpha(i)-dependent inhibition of tmACs producing cAMP for Cl(-) secretion. Since PYY or PTx did not alter sustained (epi)I(sc), signaling for K(+) secretion occurred via a Galpha(i)-independent mechanism. Presence of multiple sAC variants in colonic epithelial cells was supported by domain-specific antibodies. Responses to specific activators and inhibitors suggested that protein kinase A was not involved in activating peak or sustained components of (epi)I(sc), but the cAMP-dependent guanine nucleotide exchange factor, Epac, may contribute. Thus beta-adrenergic activation of electrogenic Cl(-) and K(+) secretion, respectively, required tmAC- and sAC-dependent signaling pathways.

Interpreting routine biochemistry in those aged over 65 years: a time for change

In clinical practice, routine biochemistry tests are often performed for diagnostic or screening purposes. We reviewed papers that have reported reference values for people older than 65 years with or without overt health problems. Wider intervals have generally been reported for sodium, potassium, calcium and C-reactive protein (CRP) in the elderly. Higher levels of creatinine and lower levels of total cholesterol (TC) and serum albumin (SA) are observed with ageing. Elderly people have been found to be at greater risk for overt abnormalities in sodium, potassium, creatinine, TC, SA and CRP. The consequences of these abnormalities could be severe. For instance, even mild hyponatremia was associated with increased risk of mortality, disability and myocardial infarction. Mild hypernatremia was associated with severe disability. Mild increases in CRP levels were associated with an increased risk of sarcopenia, disability, cardiovascular disease and cognitive decline. Mild decreases in TC levels were associated with an increased risk of disability or mortality, and mild decreases in SA were associated with an increased risk of mortality, disability, sarcopenia and frailty. Nutritional factors could not wholly explain these effects. Modified biochemical reference values are required for elderly patients, as biochemical results can serve as markers of vulnerability to age-related diseases, linked to metabolism. Careful diagnosis and corrective interventions are needed for patients in this age group.