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Mycobacterium Tuberculosis Lymphoma

CHAPTER 5

DIAGNOSIS

ABSOLUTE CRITERIA:

The absolute criteria's for the diagnosis of mycobacterium tuberculosis are: (4)

1) The culture of mycobacterium tuberculosis.

2) The detection of mycobacterium DNA by positive polymerase chain recognition.

3) The positive guinea-pig inoculation.

RELATIVE CRITERIA:

The relative criteria's for the diagnosis of mycobacterium tuberculosis are: (4)

1) The well-matched history and clinical signs.

2) The compatible histopathology.

3) The positive tuberculin test.

4) The existence of acid fast bacilli in the lesion.

5) The occurrence of active proven tuberculosis somewhere else in the body.

6) The positive response to specific antituberculous treatment.

TUBERCULIN TEST:

Tuberculin test is a result of delayed type hypersensitivity to mycobacterial antigens, release by T lymphocytes, after purified protein derivative (PPD) injection. (9)

Tuberculin sensitivity develops in 95 percent of patients, around 2 to 10 weeks following infection with mycobacterium tuberculosis and present lifelong. (9)

Tuberculin test is not specific, so a positive test can result from BCG vaccination, clinical or subclinical infections and from environmental myocbacteria. Conditions like malnutrition, malignancy such as lymphoma, acute viral infections, sarcoidosis and miliary tuberculosis may decrease delayed hypersensitivity reaction. This type of decrease hypersensitivity reactions may cause the deceptive negative type tuberculin reactions. (4)

MANTOUX TEST:

Mantoux test is usually performed by injecting 1 unit of purified protein derivative intradermally over the volar aspect of the forearm. Correct injection show a discrete, pale elevation of the skin and a wheal of 6 to 10 mm diameter. (46) After 48 to 72 hours check and measure the size of the area of induration. Serial testing may start with 1 TU, followed by 10 TU and 100 TU if negative. (4)

The results interpreted as follows:

DIAMETER OF INDURATION CONCLUSION

5-10 mm Suspicious

> 10 mm positive

> 15 mm Strongly positive

MOLECULAR GENETICS OR POLYMERASE CHAIN REACTION (PCR):

Polymerase chain reaction is a technique in which a multitude of nucleotide sequence of a single copy of a target sequence of the bacillus can be obtained in a few hours, by using a genome amplification technique. PCR can detect and identify the presence of Mycobacterium tuberculosis in a pathological specimen with in 24 to 48 hours. PCR has poor sensitivity around 80% and its specificity is from 97% to 98%. (21)

Nucleic acid amplification (NAA) can be used directly to clinical spsecimens, such as sputum so thas why they are also called Direct amplification test.

Thes tests categorized as:

1) Commercial kits

2) In house assays.

1) Commercial kits:

It include the:

1) The Amplicor MTB tests (roche Diagnostic systems,Branchburg,NJ).

2) The Amplified mycobacterium tuberculosis direct test MTD (Gen-probe,inc,San Diego, CA).

3) The BD probe Tec ET assay (Becton Dickinson Biosciences,sparks, MD).

The Amplicor and MTD tests are FDA approved. (48)

2) In house assays:

These tests are laboratory developed polymerase chain reaction (PCR) assays; they vary significantly in their design and methods. (48)

Polymerase chain reaction in vitro has been gradually more used in recent years to diagnose the mycobactereial DNA in skin specimens from patients with lupus vulgaris, papulonecrotic tuberculid and nodular vasculitis. (47)

ADVANTAGES:

1) Reduction in the time required for diagnosis in those cutaneous lesions where bacteria can be culture without difficulty, and may be predominantly helpful in paucibacillary lesions such as lupus vulgaris. The PCR takes few days while culture takes al least 2 to 4 weeks. (4)

2) This procedure can be used in variety of specimens including archival formalin-fixed tissue, where cutaneous tuberculosis is considered as one of the diagnosis. (4)

DISADVANTAGE:

1) The pitfall lies in its sensitivity, tissue samples containing bacterial DNA may be positive for the reason of bacteraemia and not because the organism involved in the pathogenesis. (4)

2) In house PCR tests have inconsistent results, therefore have limited clinical use. Commercial assays are standardized and produce more consistent results. (48)

3) This delicate technique, which requires sophisticated, costly equipment, is limited to research. (21)

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