A 26-year-old woman is brought to the emergency department after a near-syncope episode. The patient began feeling dizzy and lightheaded while at work at a skilled nursing facility where she is a patient care assistant. She had no chest pain, palpitations, or dyspnea. A nearby coworker helped her to the ground. The patient has had chronic diarrhea with 10-12 nonbloody, watery bowel movements per day, which are often associated with abdominal cramping. The diarrhea occasionally awakens her at night. Temperature is 37.1 C (98.8 F), blood pressure is 112/71 mm Hg supine and 91/50 mm Hg upright, and pulse is 94/min. Heart sounds are normal without murmur. Lung auscultation is unremarkable. The abdomen is soft, nondistended, and without tenderness. Bowel sounds are normal. Stool guaiac is negative. Laboratory testing shows hypokalemia and metabolic alkalosis. Intravenous fluids and electrolyte supplements are started. Colonoscopy reveals areas of dark brown mucosal pigmentation in the proximal colon. Which of the following findings would also be expected in this patient?
The patient's presentation is concerning for factitious diarrhea, specifically laxative abuse. Factitious diarrhea has a female predominance, and most patients are employed in the health care field and have a history of multiple hospitalizations. Diarrhea associated with laxative abuse is typically described as watery, frequent (10-20 bowel movements daily), and voluminous. Nocturnal bowel movements and abdominal cramps are common accompanying symptoms.
Although diarrhea (including factitious diarrhea) can lead to metabolic acidosis, metabolic alkalosis is a common and classic finding in laxative abuse. Several mechanisms likely contribute, including the profound hypokalemia as a result of increased loss of potassium in the stool. This then impairs chloride reabsorption and affects chloride-bicarbonate exchange, increasing serum bicarbonate concentrations (metabolic alkalosis). Patients may also have hypermagnesemia if a magnesium-containing laxative is used.
Diagnosis is supported by a positive stool screen for diphenolic (eg, bisacodyl) or polyethylene-containing laxatives. Diagnosis is further suggested by the characteristic colonoscopy finding of melanosis coli, which is dark brown discoloration of the colon with pale patches of lymph follicles that can give the appearance of alligator skin. Melanosis coli can develop within a few months of the onset of regular laxative ingestion and can similarly disappear if laxative use is discontinued. If melanosis coli is not seen on gross inspection, histological examination may demonstrate the pigment in the macrophages of the lamina propria.
(Choice A) In addition to diarrhea, carcinoid syndrome (which would cause elevated urine 5-hydroxyindoleacetic acid levels) presents with cutaneous flushing, venous telangiectasia, bronchospasm, and cardiac valvular abnormalities.
(Choice B) Although VIPomas are associated with diarrhea during fasting and dehydration, patients typically describe tea-colored stools and have hypokalemia with hypochlorhydria. VIPomas are not associated with melanosis coli.
(Choice C) Patients with low cortisol levels (eg, adrenal insufficiency) may have hypotension and chronic diarrhea; however, hyponatremia, hyperkalemia, and metabolic acidosis are the common metabolic abnormalities associated with the condition.
(Choice D) Clostridium difficile–associated diarrhea is associated with the healthcare setting (eg, antibiotic exposure). However, classic findings on colonoscopy are bowel wall edema, erythema, and friability (eg, pseudomembranous colitis), not melanosis coli.
(Choice E) Parasitic causes of persistent diarrhea, including Giardia, Cryptosporidium, and Entamoeba histolytica, are more common in patients with a history of immunosuppression or travel. None of them cause melanosis coli.
Educational objective:
Laxative abuse is characterized by frequent, watery, nocturnal diarrhea. The diagnosis is suggested by a positive laxative screen or colonoscopy with characteristic findings of melanosis coli (dark brown discoloration with pale patches of lymph follicles).