What investigations should be ordered for a suspected leprosy patient before initiating Multi-Drug Therapy (MDT)?

Pre-MDT Investigations for Suspected Leprosy

The essential pre-treatment workup for suspected leprosy should include clinical classification through skin examination and slit-skin smear for bacteriological index, along with baseline laboratory tests to assess organ function and screen for contraindications to MDT components.

Clinical Assessment and Classification

Perform a thorough skin examination to classify the disease as paucibacillary (PB) or multibacillary (MB), as this determines MDT regimen duration and components. Document:

• Number, distribution, and morphology of skin lesions
• Presence of nerve thickening or tenderness
• Sensory loss in affected areas
• The clinical spectrum (indeterminate, tuberculoid, borderline, or lepromatous)

Accurate classification is critical since PB and MB leprosy require different treatment durations, though misclassification remains common, particularly in borderline cases 1.

Bacteriological Examination

Obtain slit-skin smears from multiple sites (typically 4-6 sites including active lesions and earlobes) to determine the bacteriological index (BI):

• This helps confirm MB versus PB classification
• Provides baseline BI for monitoring treatment response
• The morphological index (MI) indicates viable bacilli

The BI is essential for proper classification, with positive smears indicating MB disease requiring longer treatment 1, 2.

Histopathological Confirmation

Perform skin biopsy in diagnostically uncertain cases:

• Take biopsy from the active edge of a representative lesion
• Send for routine histopathology to confirm diagnosis and classify disease spectrum
• Histopathology is particularly valuable when clinical and bacteriological findings are discordant

Clinicopathological concordance occurs in only 60% of cases, with maximum disparity (52.9%) in borderline spectrum patients, making biopsy crucial in doubtful cases 1.

Baseline Laboratory Investigations

Order the following baseline tests before initiating MDT:

Essential Blood Work

• Complete blood count (CBC) with differential - to detect baseline anemia or leukopenia that may worsen with dapsone
• Liver function tests (AST, ALT, bilirubin, alkaline phosphatase) - rifampicin can cause hepatotoxicity
• Renal function tests (serum creatinine, blood urea nitrogen) - to establish baseline kidney function
• Glucose-6-phosphate dehydrogenase (G6PD) levels - dapsone can cause hemolysis in G6PD-deficient patients

These baseline values are critical for monitoring drug toxicity during treatment 1.

Additional Screening

• Pregnancy test in women of childbearing age - rifampicin may reduce contraceptive efficacy
• HIV screening - based on risk factors and local prevalence, as immunosuppression affects disease presentation and treatment response

Nerve Function Assessment

Document baseline nerve function:

• Perform voluntary muscle testing (VMT) for motor function
• Test sensory function using monofilaments or ballpoint pen
• Measure nerve thickness at common sites (ulnar, median, radial cutaneous, common peroneal, posterior tibial)
• Document any existing deformities or disabilities

This baseline assessment is essential for detecting nerve damage progression and differentiating treatment complications from disease progression 3.

Screening for Contraindications

Assess for specific drug contraindications:

• History of sulfonamide allergy (contraindication to dapsone)
• Severe anemia or methemoglobinemia (relative contraindication to dapsone)
• Severe hepatic impairment (caution with rifampicin)
• Psychiatric history (clofazimine-related depression, though rare)

Optional Investigations

Consider in specific clinical scenarios:

• Lepromin test - may help differentiate late relapse from reinfection in cases developing new lesions years after MDT completion 3
• Nerve conduction studies - in pure neuritic leprosy or when nerve involvement is prominent
• Chest X-ray - if pulmonary symptoms present or for baseline in elderly patients

Common Pitfalls to Avoid

Do not delay treatment while awaiting biopsy results if clinical diagnosis is clear - leprosy is a clinical diagnosis and MDT should be initiated promptly to prevent nerve damage 1.

Do not misclassify borderline cases - when in doubt between PB and MB, treat as MB since undertreatment carries greater risk than overtreatment 2.

Do not omit baseline BI documentation - this is essential for monitoring treatment response, as the morphological index should become negative after 6 months of treatment and mean BI should fall by approximately 1.0 after one year 1.

Do not forget to screen household contacts - approximately 8.3% of patients have a definite contact history, and contact tracing is an important public health measure 1.

Practical Algorithm

1. Clinical examination → classify as PB or MB based on number of lesions and nerve involvement
2. Slit-skin smear → confirm classification with BI
3. Baseline blood tests → CBC, LFTs, renal function, G6PD
4. Skin biopsy → only if diagnosis uncertain or classification unclear
5. Nerve function assessment → document baseline for future comparison
6. Initiate appropriate MDT → PB-MDT (6 months) or MB-MDT (12 months) based on classification

The goal is to initiate treatment promptly while ensuring adequate baseline documentation for monitoring treatment response and adverse effects 1, 4.