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
| Category | Condition | Diagnostic Tests |
|---|---|---|
| Endocrine diseases | Hyperthyroidism Addison’s disease Panhypopituitarism Diabetes mellitus | Thyroid-stimulating hormone, T4 ACTH-stimulation test, cortisol ACTH-stimulation test, TSH Blood glucose, glycosylated hemoglobin |
| Endocrine tumor syndromes | MEN-1 (Wermer syndrome)Hyperparathyroidism Pancreatic endocrine tumors Pituitary tumors (Also may have adrenal cortical tumors, thyroid adenomas) MEN-2a (Sipple syndrome) Medullary thyroid cancer Pheochromocytoma Hyperparathyroidism MEN-2b (same as MEN-2a + neuromas, Marfanoid phenotype) | Parathormone Gastrin, VIP, insulin, glucagon Prolactin, growth hormone, ACTH Calcitonin Urine metanephrine Parathormone |
| Hematologic diseases | Leukemia, lymphoma Multiple myeloma | Complete blood count Serum protein electrophoresis |
| Immune system disorders | AIDS Amyloidosis Common variable immunodeficiency IgA deficiency | HIV serology Mucosal biopsy Immunoglobin levels |
| Heavy metal poisoning | Heavy 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.
