Mid-Borderline (BB) Leprosy
Mid-borderline leprosy (BB) is the “true” borderline form in the Ridley-Jopling classification. It is the most unstable state of the disease, located directly in the middle of the immunological spectrum between Tuberculoid (TT) and Lepromatous (LL) leprosy.
Clinical Features
- Lesions: Numerous, asymmetrical plaques that are often annular (ring-shaped).
- Hallmark Appearance: The “punched-out” lesion—a central clearing with a distinct, sharp inner margin and a poorly defined, fuzzy outer margin.
- Nerve Involvement: Moderate, asymmetrical, and often associated with sensory loss within the lesions.
Diagnostic & Management Pearls
| Aspect | Details |
|---|---|
| Bacteriology | Bacterial index is moderate; slit-skin smears are typically positive. |
| Treatment | Multidrug Therapy (MDT)—specifically the multibacillary (MB) regimen (Dapsone, Rifampin, Clofazimine) for 12 months. |
High-Yield Exam Pearl:
- Reactions: Patients in the borderline spectrum are at the highest risk for Type 1 (Reversal) reactions, which are delayed-type hypersensitivity reactions that can cause rapid nerve damage and require immediate systemic corticosteroids.
- Clinical Tip: Look for the “punched-out” lesion on exams—if the inner edge is sharp and the outer edge is hazy, think BB Leprosy.