Laboratory Studies
Routine laboratory values are often abnormal. Initial laboratory studies routinely obtained include the following:
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Baseline CBC with differential, platelets, and erythrocyte indexes
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Electrolytes - Sodium, potassium, chloride, calcium, magnesium, iron
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Vitamin levels (usually folate and vitamin B-12 with its metabolic derivatives, homocysteine and methylmalonic acid); thiamin (vitamin B-1), pyridoxine (vitamin B-6), and carotene (provitamin A) levels may help identify rapidly reversible deficits and rule out alternative diagnoses.
Other baseline labs should target some of the differential diagnosis variants and include rapid plasma reagent and HIV testing, erythrocyte sedimentation rate, complement C3 and C5, antinuclear antibody, and angiotensin-converting enzyme levels. Also obtain baseline liver function tests, thyroid function tests, and random cortisol level. Extend endocrinologic workup (free testosterone, luteinizing hormone, follicle-stimulating hormone) on an individual basis to rule out pituitary gland or, more commonly, hypothalamic involvement.
Nonspecific results supportive of steatorrhea include decreased serum cholesterol and carotene levels, decreased iron levels, elevated prothrombin time, and low serum albumin as a result of a combination of the protein-losing enteropathy, decreased absorption of amino acids, and decreased hepatic synthesis.
Multifactorial normocytic hypochromic anemia is present in 90% of patients and is caused by chronic infection and malabsorption with decreased iron, vitamin B-12, and folate.
Not infrequently, thrombocytosis is present with counts of greater than 1 million/mL. This may be the basis for a hyperviscosity syndrome (with exacerbation of cardiac disease and stroke). Both anemia and thrombocytosis reverse with specific antibiotic treatment for Whipple disease.
Imaging Studies
Radiology
Of patients with Whipple disease with GI upset, 85% have abnormal results on upper GI series. More than 50% of these patients present with bowel dilation with or without prominent mucosal folds of the duodenum and jejunum. In 60% of these patients, flocculation and segmentation of barium also is reported.
Other findings include dilatation of the proximal ileum, stomach with thickened nodular folds, and possibly edema of the colon on barium enema. All of these findings are nonspecific; they also may be found in other diseases such as celiac sprue and lymphoma.
Various imaging studies reveal enlarged retroperitoneal and mediastinal lymph nodes in 10% of patients with Whipple disease.
Neuroimaging
Neuroimaging is largely nonspecific. CT scan and MRI with and without contrast may reveal nondiagnostic abnormalities including atrophy, hydrocephalus, mass lesions with contrast enhancement, ring-enhancing lesions, and other focal changes, including white matter changes with no mass effect, suggesting demyelination.
Other Tests
Specific tests for malabsorption and biliary salts metabolism
Specific tests indicative of steatorrhea (90% of patients with Whipple disease have malabsorption) include qualitative or 72-hour quantitative stool analysis and absorption of D-xylose (with decreased fractional absorption detected by low serum and urinary levels). [16]
Bile salt metabolism testing reveals an increase in the deoxycholic acid-to-cholic acid ratio after intravenous challenge with taurocholate (ie, the inverse of the normal response).
Electrodiagnostic testing
No diagnostic/specific EEG pattern has been described for CNS-WD. EEG may be normal, show focal or generalized slow wave activity, or identify irritative foci with spike activity.
Electromyography (EMG) of the muscles involved in OFSM has revealed 400-millisecond bursts of bilateral rhythmic activity. The activity originates from the level of CN VII and spreads rostrally to involve the muscles of mastication and caudally to involve muscles of the neck, arms, and legs.
Cerebrospinal fluid studies
CSF is frequently abnormal (high protein, > 5 WBC, intrathecal synthesis of IgA). In patients who carry a diagnosis of Whipple disease, nonspecific inflammatory markers in CSF have been reported as useful surrogates to monitor response and durability of remission. More specific testing of the CSF is required for a positive diagnosis, such as PAS staining, EM, and PCR.
CSF PCR should be considered in all patients with Whipple disease; as it gains acceptance as a useful tool for assessing CNS involvement, it represents the most sensitive tool in evaluating response to antibiotic treatment and early detection of relapse. [21] Termination of a long course antibiotic treatment in a patient with Whipple disease who experienced a good clinical response should be based ultimately on CSF PCR analysis alone.
Procedures
The diagnosis of Whipple disease is made by demonstrating characteristic lesions in tissue obtained from biopsy of significant organs (defined as organs usually known to be involved in Whipple disease and responsible for some of the complaints and/or signs noted on examination).
The medical practitioner should plan significant organ biopsy with PAS staining, EM analysis, and PCR of the tissue sample.
For patients with GI complaints, peroral GI biopsy should be the initial diagnostic method of choice. It reveals foamy macrophages containing PAS-positive, gram-positive bacilli in the lamina propria of the mucosa of the small intestine.
Studies reviewing patients with Whipple disease and GI complaints revealed only a 50% sensitivity of multiple (2-3) peroral GI biopsies. The review of patients with CNS-WD revealed a higher sensitivity of 70%, which is due in part to a sampling effect, since these patients are less likely to be diagnosed with CNS-WD without a positive peroral GI biopsy.
Consider all patients with CNS-WD for a peroral GI biopsy as part of their initial diagnostic workup.
PAS-positive macrophages in the lamina propria of the colon and rectum are nondiagnostic, since they have been reported in healthy people and in patients with histiocytosis, melanosis coli, or pneumatosis intestinales.
PAS-positive macrophages in lymph node biopsy alone, not corroborated by other significant tissue biopsy results, is not diagnostic, since this can be a common finding in tuberculosis, sarcoidosis, Gaucher disease, and berylliosis.
Lumbar puncture: CNS involvement can be demonstrated quite well with CSF analysis; PAS staining of cellular material may be adequate, or the diagnosis may be confirmed with PCR when PAS staining is inconclusive.
Brain biopsy [22] is a last resort in a patient with a nonspecific focal lesion amenable to biopsy in whom the diagnosis cannot be made by testing other sites (eg, GI biopsy) or by CSF analysis.
Histologic Findings
Macrophages containing PAS-positive, gram-positive bacilli have been found in various body tissues of patients with Whipple disease, including heart and heart valves, CNS and CSF, lung, spleen, Kupffer cells (ie, cells with functional role of macrophages in the liver), pancreas, muscle, bone marrow, kidney, lymph nodes, and synovial membranes.
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The PAS-positive material found in macrophages represents remnants of the cell walls of the phagocytosed bacilli. These bacilli stain gram positive and acid-fast negative. Whipple disease bacillus has a distinct wall and an outer capsule and measures approximately 0.5-1.5 mm. These bacilli, despite typically being regarded as intracellular pathogens, also have been found as PAS-positive, rod-shaped bacteria in the extracellular environment.
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CNS-WD has a predilection for the periaqueductal gray matter, hypothalamus, hippocampus, basal ganglia, cerebellum, and cerebral cortex. Whipple disease bacillus usually is found at the site of involvement along with a specific inflammatory response.
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The gross pathologic features of CNS-WD are generalized atrophy and small, chalky nodules or granulomas as large as 2 mm in diameter scattered diffusely in the grey matter of the cerebral and cerebellar hemispheres and in the periventricular and periaqueductal regions. The changes are patchy and usually are surrounded by totally normal areas of the brain.
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The involvement of periaqueductal gray matter is thought to be responsible for hydrocephalus observed in some patients.
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The microscopic appearance of the granulomatous changes reveals strongly PAS-positive macrophages surrounded by large reactive astrocytes. In more advanced cases, the PAS-positive cellular infiltrate may extend in the white matter and may be associated with demyelination and neuronal death with formation of large vacuoles; with more severe extension, the PAS-positive infiltrate may burst into the subarachnoid space. All strongly PAS-positive areas of the brain reveal specific trilamellar appearance of T whippelii bacilli and bacillary debris on EM.
