When should Thwaites, Lancet, and Marais scores be used in tuberculosis (TB) management?

When to Use Thwaites, Lancet and Marais Scores in Tuberculosis Management

Thwaites and Lancet consensus scoring systems should be used primarily for differentiating tuberculous meningitis (TBM) from other forms of meningitis, particularly in resource-limited settings where advanced diagnostic capabilities may be unavailable.

Thwaites Score

• Primary use: Differentiating TBM from bacterial meningitis
• Best application: In settings of subacute meningitis (symptoms 5-30 days)
• Interpretation: Scores ≤4 suggest high probability of TBM

Lancet Consensus Scoring System

• Primary use: More comprehensive classification of TBM probability
• Best application: In both subacute and chronic meningitis cases
• Classification categories:
  • Definite TBM
  • Probable TBM (score ≥12)
  • Possible TBM
  • Non-TBM
• Advantage: Better at differentiating TBM from fungal, viral, and unknown etiologies of meningitis 1

Marais Score

While not extensively covered in the evidence provided, the Marais criteria is part of the Lancet consensus scoring system for TBM diagnosis.

Comparative Performance

• Both scoring systems show moderate agreement with expert clinical diagnosis (Kappa statistic = 0.53) 2
• Lancet scoring system demonstrates fair diagnostic accuracy (AUC-ROC = 0.738) with:
  • Sensitivity of 50%
  • Specificity of 89.3% 1
• Thwaites system shows poorer diagnostic accuracy for distinguishing TBM from non-TBM etiologies in subacute and chronic meningitis

Clinical Application Algorithm

1. Initial presentation with meningitis symptoms:

   • Apply both scoring systems for complementary information
   • Consider duration of symptoms (acute vs. subacute vs. chronic)

2. For suspected bacterial meningitis vs. TBM:

   • Prioritize Thwaites score for initial differentiation
   • Scores ≤4 suggest TBM; initiate anti-TB treatment if clinical suspicion is high

3. For subacute/chronic meningitis with multiple possible etiologies:

   • Use Lancet consensus scoring system for more comprehensive assessment
   • Consider "Definite," "Probable," or "Possible" TBM categories to guide management

4. When scores are discordant:

   • Prioritize clinical judgment in a tertiary care setting
   • Note that 11% of patients classified as TBM by Thwaites may be classified as "Non-TBM" by Lancet 2

Important Caveats

• Neither scoring system should replace microbiological confirmation when available
• Treatment decisions should not be delayed while awaiting culture results if clinical suspicion for TBM is high 3
• Both scoring systems have limitations in settings without CT and MRI facilities 2
• Significant overlap occurs between TBM and other etiologies with both scoring systems 1
• Consider the local epidemiology of TB and other causes of meningitis when interpreting scores

Treatment Considerations

If TBM is diagnosed or strongly suspected based on scoring systems:

• Initiate prompt combination anti-TB chemotherapy
• Standard regimen includes isoniazid, rifampin, pyrazinamide, and ethambutol
• Individualized case management should be provided with coordination with local health departments 3

These scoring systems should be used as adjuncts to clinical judgment, particularly in resource-limited settings where definitive microbiological diagnosis may be delayed or unavailable.