Diagnostic Index of Thwaites et al for Tuberculous Meningitis in Adults From a Developing Country with High Prevalence of Tuberculosis

 

NOTE: The study was performed in Ho Chi Minh City and involved a population with a high prevalence of tuberculosis. The diagnostic resources were limited, and factors such as survival without antituberculous medications were used for categorizing patients.

 

NOTE: This might be more accurate for distinguishing tuberculous from nontuberculous meningitis, rather than from bacterial meningitis. Classification as bacterial meningitis included sterile blood and CSF cultures with full recovery at 3 months without antituberculous therapy. In theory viral meningitis would not be included because selection criteria included presence of neutrophils and a low glucose in the CSF.

 

Patients: immunocompetent adults from 16 to 64 years of age

 

Parameters:

(1) age in years

(2) blood white blood cell count

(3) number of days ill

(4) number of white blood cells in the CSF

(5) percent neutrophils in the CSF

Parameter	Finding	Points
age in years	>= 36 years	2
	< 36 years	0
blood WBC count	>= 15,000 per µL	4
	< 15,000 per µL	0
number of days ill	>= 6 days	-5
	< 6 days	0
CSF total WBC count	>= 900	3
	< 900	0
percent neutrophils in CSF	>= 75%	4
	< 75%	0

 

diagnostic index =

= SUM(points for all 5 parameters)

 

Interpretation:

• minimum index: -5

• maximum index: 13

• A low index value favors the diagnosis of tuberculous meningitis.

 

Diagnostic Index	Interpretation
<= 4	tuberculous
> 4	nontuberculous, presumed bacterial

 

Performance:

• In the study population: sensitivity 97%, specificity 91%

 

Limitations:

• The prevalence of HIV infection will affect the performance of the index. A person with untreated HIV can have a high rate of tuberculosis as well as opportunistic infections. In the study population 66 of 251 patients were tested (those with clinical risk factors for HIV) for HIV antibodies with 8 positive (about 12% of those tested).