Leprosy is a chronic infectious disease caused by M.Leprae- an acid fast bacilli.
The route of transmission is unclear but is thought to be via nasal droplet infection and contact transmission.
The organism prefers cooler temperature (body surface temperature is less than core body temperature) and hence it mainly involves skin and peripheral nerves. It is obvious that the most common internal organ involved in males is testis (in females, it is liver).
The outcome of the infection primarily depends upon immune status of the person.
If a person has excellent immunity, disease will not occur.
If the immunity is undecided (mostly in children), it leads to indeterminate leprosy.
RIDLEY JOPLING CLASSIFICATION
BT BB BL
(TT-tuberculoid, BT-borderline tuberculoid, BB-borderline, BL-borderline lepromatous, LL-lepromatous.)
As the bacilli reach the skin dermis, it is engulfed by dermal macrophages and the schwann cells of peripheral nerves. These macrophages goes to the lymph nodes and activates T cells and B cells. The relative proportion of activated T cell and B cell in an individual determine the outcome of the disease because T cells are able to kill the bacilli (hence, represent good immunity), while B cells produce antibodies which doesn’t kill bacilli (hence, represent poor immunity).
Conclusion- in TT mainly T cells are activated and in LL mainly B cells are activated.
This is also evident in biopsy of the lesion. The T cells lead to GRANULOMA formation while B cells which do not kill antibodies results in macrophages heavily laden with bacilli, known as foam cell/lepra cell. The arrangement of bacilli in macrophages is typical and is known as CIGAR SHAPED BODIES OR GLOBI ARRANGEMENT. So, as we go from TT to LL in biopsy, the granuloma formation decreases and foam cell increases.
As per WHO, the cardinal signs of leprosy are-
- Anesthetic skin patch
- Peripheral nerve thickening
- AFB in split skin smear
SKIN MANIFESTATION OF TT
In TT because of the granuloma formation around the nerve, there is compression of the superficial cutaneous nerve leading to anaesthesia.
(remember, lepra bacilli prefers cooler temperature. Hence, it affects superficial cutaneous sensory nerves and not deep nerves. Since, proprioception and vibration are the sensations carried by deep nerves, they are intact).
The TB granuloma is toxic to melanocytes and hence results in HYPOPIGMENTED PATCH.
NOTE- THERE IS ONLY SINGLE SKIN LESION AND SINGLE THICKENED NERVE IN TT.
The skin lesion in TT is a hypopigmented anaesthetic macule with a well defined elevated border (SAUCER LESION).
SKIN MANIFESTATION OF BB
The number of lesions is more.
The lesion is –
SKIN MANIFESTATION OF LL
Since in LL immunity is poor (i.e only B cells are formed), there is no granuloma formation and hence no nerve compression (no hypopigmentation, no sensation loss in early stage). These patient remain asymptomatic in the early phase of the disease but they are highly infectious. This is one of the reason why it is difficult to eradicate leprosy and we have to do active case detection campaign.
Bilaterally thick nerve is seen later in the course of disease because of nerve invasion and sensation is lost in later stages (the typical GLOVE STOCKING anaesthesia– sensations are lost distal to wrist and ankle).
LATERAL MADAROSIS can be also seen(loss of outer 1/3rd of eyebrow)
Nodular LL- also known as leonine leprosy. TYPICAL LEONINE FACIES IS SEEN.
As we give the patient MDT, there is destruction of bacilli. This leads to a hypersensitivity response in the body. Since there are two types of immunity involved in leprosy- B cell and T cell, there are corresponding hypersensitivity reaction.
T cell hypersensitivity
B cell hypersensitivity
Type 1 lepra reaction
Type 2 lepra reaction
Seen in BT and BB
Seen in BL and LL
Cell mediated type 4 hypersensitivity
Antibody mediated type 3 hypersensitivity
Inflammation of the existing lesions(redness and pain). Neuritis can also occur.
ERYTHEMA NODOSUM LEPROSUM ENL-New tender red nodules.(Ag-Ab complexes deposit in various tissues causing vasculitis,glomerulonephritis.)
TREATMENT -oral steroids
In cases of recurrent ENL, drug of choice is clofazimine.
It is an intradermal test used to know the immune status (cell mediated immunity) of the patient.
The response to id injection is typically biphasic.
- Early reaction of Fernandez– occurring in 48-72 hrs and consists of erythema and induration. It carries a little significance.
- Late reaction of mitsuda- occurring in 3-4 weeks and consists of skin nodule. This reaction indicates cell mediated immunity (CMI) mounted against injected antigen (and not preexisting delayed type hypersensitivity). Thus it distinguishes a person who can mount CMI against lepra baciili and the one who can not.
It is NOT DIAGNOSTIC.
The test is positive in TT (good immunity) and negative in LL(poor immunity).
It is used for prognosis. Conversion of lepromin positivity during treatment is a sign of good prognosis.
The most common peripheral nerve involved is ulnar nerve. This may lead to claw hand.
Involvement of median nerve at wrist will lead to carpel tunnel syndrome.
Most common nerve involved in lower limb is posterior tibial.
Most common cranial nerve involved is facial (lower motor neuron palsy affecting mainly upper fibres). Orbicularis oculi muscle is affected leading to LAGOPHTHALMOS. Orbicularis oris is SPARED.
NOTE– in cases of neural Hansen (no skin lesion), nerve biopsy is taken. We do not prefer to take biopsy from ulnar nerve as it has motor supply and might cause permanent hand deformity. Therefore we take biopsy from radial cutaneous nerve which is sensory.
CLASSIFICATION OF PATIENTS PB (paucibacillary) and MB (multibacillary)
Rest 27 days
R-600 mg+ D-100 mg+ C-300 mg
C-50 mg+ D-100 mg
For children 10-14 years
R-450 mg+ D-50 mg+ C-150 mg
C-50 mg+D-50 mg
For children <10yrs/<40kg
R-10 mg/kg+ D-2 mg/kg+ C-6 mg/kg
C-1 mg/kg+ D-2 mg/kg
Duration – for PB- 6 months and for MB- 12 months (FOR ALL CASES).
Thank you for reading. Hope you liked it!
-Made by Mansi Nahar (GMC, Nagpur)