Classifications of diarrheal diseases

Classifications of diarrheal diseases

Because the symptom of diarrhea has such a broad differential diagnosis, it is useful to classify the type of diarrhea to restrict the differential diagnosis to a more manageable number of conditions. Three helpful classification schemes include:

  • • Acute versus chronic (4 weeks or longer)
  • • Epidemiologic criteria (traveler’s, epidemic or outbreak, acquired immune deficiency syndrome [AIDS], and institutional)
  • • Stool characteristics (watery, fatty, inflammatory)

Watery stools are typically runny and lack blood, pus, or fat. Watery diarrhea is subdivided into secretory and osmotic types, depending on stool electrolyte concentrations. Fatty stools have an excess of fat, which can be shown by qualitative testing with the Sudan stain or by quantitative analysis of a timed stool collection for fat. Inflammatory diarrheas typically contain blood or pus. If not grossly evident, these characteristics can be detected by a fecal occult blood test or by staining the stool for neutrophils. Classifying diarrheas by stool characteristics enables the physician to sort quickly through more likely and less likely diagnoses. This scheme is thus very useful in chronic diarrheas in which construction of a reasonable differential diagnosis can lead to more appropriate testing and more rapid diagnosis.

Tests for Evaluation of Systemic Diseases Associated with Chronic Secretory Diarrhea

CategoryConditionDiagnostic Tests
Endocrine diseasesHyperthyroidism
Addison’s disease
Diabetes mellitus
Thyroid-stimulating hormone, T4
ACTH-stimulation test, cortisol
ACTH-stimulation test, TSH
Blood glucose, glycosylated hemoglobin
Endocrine tumor syndromesMEN-1 (Wermer syndrome)Hyperparathyroidism
Pancreatic endocrine tumors
Pituitary tumors
(Also may have adrenal cortical tumors, thyroid adenomas)
MEN-2a (Sipple syndrome)
Medullary thyroid cancer
MEN-2b (same as MEN-2a + neuromas, Marfanoid phenotype)
Gastrin, VIP, insulin, glucagon
Prolactin, growth hormone, ACTH
Urine metanephrine
Hematologic diseasesLeukemia, lymphoma
Multiple myeloma
Complete blood count
Serum protein electrophoresis
Immune system disordersAIDS
Common variable immunodeficiency
IgA deficiency
HIV serology
Mucosal biopsy
Immunoglobin levels
Heavy metal poisoningHeavy metal screen

ACTH, Adrenocorticotropic hormone; AIDS, acquired immune deficiency syndrome; HIV, human immunodeficiency virus; Ig, immunoglobulin; MEN, multiple endocrine neoplasia; T4, thyroxine; TSH, thyroid-stimulating hormone; VIP, vasoactive intestinal polypeptide.


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