Leprosy: Understanding Tuberculoid (TT) and Lepromatous (LL) Forms

What is TT and LL in Leprosy?

TT (Tuberculoid Leprosy) and LL (Lepromatous Leprosy) represent the two polar, most distinct forms of Hansen's Disease, commonly known as leprosy, characterized by differing immune responses to the bacterium Mycobacterium leprae.

Understanding Leprosy (Hansen's Disease)

Leprosy is a chronic infectious disease caused by the slow-growing bacterium Mycobacterium leprae. It primarily affects the skin, peripheral nerves, upper respiratory tract, eyes, and testes. The disease is curable with multidrug therapy (MDT), and early diagnosis and treatment are crucial to prevent disabilities. The wide range of clinical manifestations in leprosy is largely due to the varying immune responses of individuals to the Mycobacterium leprae pathogen.

The Spectrum of Leprosy

Rather than just two types, leprosy exists on a continuous spectrum, often referred to as the Ridley-Jopling classification, with Tuberculoid Leprosy (TT) and Lepromatous Leprosy (LL) as the two stable, polar ends. Between these two poles lie the "borderline" forms: Borderline Tuberculoid (BT), Mid-Borderline (BB), and Borderline Lepromatous (BL). The position on this spectrum is determined by the patient's cell-mediated immune response (CMIR) to Mycobacterium leprae.

Tuberculoid Leprosy (TT)

Tuberculoid leprosy (TT) represents the pole of the spectrum where the host's cellular immunity to Mycobacterium leprae is strong and effective.

• Clinical Presentation:
  • Skin Lesions: Typically characterized by one or a few sharply demarcated, hypopigmented (lighter than surrounding skin) or erythematous (reddish) patches or plaques. These lesions often have raised, active borders and are usually anesthetic (numb) to touch, temperature, and pain due to nerve damage within the lesion.
  • Nerve Involvement: Early and significant involvement of peripheral nerves near the skin lesions. This often leads to palpable, thickened nerves and noticeable loss of sensation in the affected areas. Muscle weakness or paralysis can occur in areas supplied by affected nerves.
  • Bacteriology: Few or no acid-fast bacilli (AFB) are found in skin smears or biopsies (paucibacillary).
• Immune Response: Individuals with TT exhibit a robust cell-mediated immune response, effectively containing the bacterial spread. The immune system forms granulomas around the bacteria, limiting their proliferation.
• Contagiousness: TT is considered lowly contagious due due to the limited number of bacteria present.
• Prognosis: Generally good with treatment, with a lower risk of extensive disfigurement, though nerve damage can lead to permanent disability if not treated early.

Lepromatous Leprosy (LL)

Lepromatous leprosy (LL) is at the opposite end of the spectrum, where the host's cellular immunity to Mycobacterium leprae is weak or virtually absent, leading to widespread bacterial proliferation.

• Clinical Presentation:
  • Skin Lesions: Numerous, symmetrically distributed, poorly defined, shiny, often reddish or copper-colored nodules, plaques, or diffuse infiltrations. These lesions are typically not anesthetic in the early stages but can become so as nerve damage progresses. Facial involvement can lead to characteristic thickening of facial features, known as "leonine facies."
  • Nerve Involvement: Widespread, symmetrical involvement of peripheral nerves, which may not be as acutely painful or obviously thickened as in TT, but can lead to extensive and progressive sensory loss and motor weakness over time.
  • Other Organs: The bacteria can proliferate in various tissues, including the eyes (leading to blindness), upper respiratory tract (nasal collapse, hoarseness), testes (infertility), and bones.
  • Bacteriology: Abundant acid-fast bacilli (AFB) are found in skin smears and biopsies (multibacillary).
• Immune Response: Individuals with LL have a deficient cell-mediated immune response, allowing Mycobacterium leprae to multiply extensively throughout the body. While they may have a strong humoral (antibody) response, these antibodies are largely ineffective in clearing the intracellular bacteria.
• Contagiousness: LL is considered highly contagious compared to TT, due to the massive bacterial load.
• Prognosis: More severe course with a higher risk of extensive disfigurement, permanent nerve damage, and disability if not adequately treated.

Other Forms on the Spectrum

Between TT and LL, the borderline forms represent varying degrees of immunological stability and clinical presentation:

• Borderline Tuberculoid (BT): Closer to TT, with relatively few lesions, some nerve involvement, and moderate bacillary load. Can downgrade towards LL or upgrade towards TT.
• Mid-Borderline (BB): Intermediate form, with multiple lesions, significant nerve involvement, and a higher bacillary load. Immunologically unstable.
• Borderline Lepromatous (BL): Closer to LL, with numerous, poorly defined lesions, widespread nerve involvement, and high bacillary load. Tends to be immunologically unstable and can progress to LL if untreated.

Diagnosis and Treatment

Diagnosis of leprosy is primarily clinical, based on the presence of cardinal signs: definite loss of sensation in a skin patch, thickened peripheral nerves, and/or the presence of acid-fast bacilli in a skin smear. All forms of leprosy are treatable with multidrug therapy (MDT), a combination of antibiotics provided free of charge by the World Health Organization (WHO). The specific regimen and duration depend on whether the patient is classified as paucibacillary (TT, BT) or multibacillary (BB, BL, LL).

Importance of Early Diagnosis

Regardless of the form, early diagnosis and complete treatment are paramount to prevent the progression of the disease, halt nerve damage, and avoid the debilitating deformities and disabilities associated with advanced leprosy. Effective treatment also stops transmission of the disease.

Conclusion

TT and LL are the two extreme manifestations of leprosy, reflecting the host's immune system's varying ability to control Mycobacterium leprae. Tuberculoid leprosy (TT) signifies strong immunity and limited disease, while Lepromatous leprosy (LL) indicates a weak immune response and widespread bacterial proliferation. Understanding this spectrum is crucial for accurate diagnosis, classification, and effective management of Hansen's Disease.