Buruli Ulcer Workup

Updated: Feb 06, 2017
  • Author: Shannon C Brown, MD; Chief Editor: William D James, MD  more...
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Workup

Approach Considerations

Rapid diagnosis and treatment are necessary. Unfortunately, the major burden of Buruli ulcers occurs in remote rural areas, where fast and accurate testing is not available. Currently, the only available point-of-care test is microscopic detection of acid-fast bacilli (AFB), which is obtained from biopsy specimens from deep subcutaneous tissue within the ulcers, and is neither sensitive nor specific. [41] The development of point-of-care tests, such as fluorescent thin-layer chromatography, is considered a research priority by the World Health Organization (WHO). [3]

 

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Laboratory Studies

Regardless of the test or sampling method, at least two sites per suspicious lesion should be submitted to increase the sensitivity by 25% over a single specimen. [42]

Polymerase chain reaction (PCR) testing for IS2404 (and IS2606) of punch biopsy, swab, and fine-needle aspiration specimens is the criterion standard for laboratory confirmation. Studies have demonstrated swabs are more beneficial than punch biopsy specimens or fine-needle aspirations for ulcerated lesions. For nonulcerated lesions, fine-needle aspiration is preferred over a 3-mm punch biopsy sample and provides sensitivities of more than 90%. [43, 44] PCR provides results within 48 hours and has a sensitivity of 90-98%. [45, 46] PCR remains positive for as long as 40 days into the antibiotic course. Unfortunately, PCR is only available in research laboratory settings and is expensive.

A direct smear from the necrotic base of the lesion may be stained with Ziehl-Neelsen stain, revealing clumps of AFB. This method has a sensitivity of 40-50% in the ulcerative form, 60% in the nodular form, and 80% in the edematous form. [10] Improvement in the yield can be achieved by good sample collection, concentration of the specimen before smearing, good microscopy practices, and analysis of at least three separate swabs. [47]

Mycobacterium ulcerans can be cultured from ulcer exudate or fresh tissue, or by swabbing the entire undermined rim of the ulcer. The inoculums must be incubated at 30-35°C (most sources recommend 32-33°C) on Lowenstein-Jensen medium. Because the organism is a slow grower, it can take 6-8 weeks before it can be isolated by culture. [18] This method has a sensitivity of only 20-60%. [10]

Biopsy for histological evaluation has a sensitivity of 82-90%, and this technique is generally done when surgical treatment is performed or there is a paradoxical reaction. [10]

Point-of-care tests that can be deployed to clinics throughout the world are a current area of research. A new dry reagent–based PCR assay, loop-mediated isothermal amplification (LAMP) technique, [48] and reverse transcriptase RNA PCR are being researched and may be better suited for countries where Buruli ulcer is endemic. These methods have a sensitivity similar to or better than conventional PCR. [49, 50]

For patients with multiple episodes of Buruli ulcers, next-generation sequencing (NGS) techniques may be performed to distinguish relapses from reinfections. [51]

Table 1. Pros and Cons of Sampling Techniques From the WHO [37] (Open Table in a new window)

Method Pros Cons
Direct smear examination • Easy to perform at local level



• Does not require expensive materials and equipment



• Rapid results



• Uses swabs, fine-needle aspiration, and biopsy samples



• Low sensitivity (<60%)



• Needs trained personnel



• Needs external quality assurance



PCR • Results fairly rapid



• Uses swabs, fine-needle aspiration, and biopsy samples



• High sensitivity (>95%)



• Requires a sophisticated laboratory



• Expensive to perform



• Needs trained personnel



• Requires strict quality control



Culture of M ulcerans • Uses swabs, fine-needle aspiration, and biopsy samples • Requires a sophisticated laboratory



• Needs trained personnel



• Results take >8 weeks



• Low sensitivity (20-60%)



• Not useful for immediate patient management



Histopathology • Sensitivity is about 90%



• Results fairly rapid (if services are available)



• Useful in establishing differential diagnosis and monitoring unexpected response to treatment



• Requires a sophisticated laboratory



• Expensive to perform



• Needs trained personnel



• Requires invasive procedure (ie, biopsy)



 

 

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Imaging Studies

Ultrasonography can reveal the depth and extension of Buruli ulcers and can be used to follow the response to antibiotics. [52]

If osteomyelitis is suspected, then a radiologic evaluation is recommended.

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Histologic Findings

Histopathologic specimens reveal extensive coagulation necrosis in the dermal collagen and the subcutaneous fat, with destruction of cutaneous nerves, blood vessels, and adnexal structures. The necrosis may extend well beyond the edges of the ulceration. In early lesions, extracellular clumps of AFB may be seen at the base of the ulcer in the deep subcutaneous tissue. In active lesions, the inflammatory infiltrate is usually absent to mild, although a leukocytoclastic vasculitis or thrombosis of small- and medium-sized vessels may be seen. In older lesions, a granulomatous reaction occurs, with fewer organisms present, eventuating into cicatrix formation. Epidermal hyperplasia is more common in ulcerative than preulcerative lesions. [53]

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