Question
Ridel-Walker test.
Answer
The Ridley-Walker (or Ridley-Jopling) classification is the widely used histopathological/immunological spectrum classification of leprosy (caused by Mycobacterium leprae), grading disease across a spectrum based on the host’s cell-mediated immune response to the organism.
Spectrum (from strong to weak cell-mediated immunity):
- Tuberculoid leprosy (TT) — strong cell-mediated immune response, limiting the organism; few, well-defined, hypopigmented/anaesthetic skin lesions with few bacilli (paucibacillary), well-formed epithelioid granulomas on histology.
- Borderline tuberculoid (BT), Borderline (BB), Borderline lepromatous (BL) — intermediate, unstable forms across the spectrum, with progressively weaker immune containment and increasing bacillary load moving toward the lepromatous pole.
- Lepromatous leprosy (LL) — weak/absent cell-mediated immunity (Th2-skewed, antibody-dominant response, which is ineffective at controlling this intracellular pathogen), with numerous, poorly defined, symmetrical skin lesions, high bacillary load (multibacillary), and diffuse macrophage infiltration with abundant bacilli (foamy/Virchow cells) rather than organized granulomas.
- Indeterminate leprosy — an early, non-specific form that may resolve or progress to one of the above forms depending on the developing immune response.
Clinical/laboratory correlation: the position on the spectrum correlates with the lepromin skin test (positive in tuberculoid, negative in lepromatous — a delayed-type hypersensitivity test analogous to the Mantoux test, though used for classification rather than diagnosis), bacillary index on skin smear/slit-skin smear microscopy, and treatment regimen (paucibacillary vs. multibacillary WHO multidrug therapy).
Significance: this classification guides both prognosis (lepromatous disease carries a higher risk of nerve damage/deformity and is more infectious) and treatment duration/drug regimen selection under the WHO multidrug therapy programme.