CNS Infections- Leprosy Flashcards
(43 cards)
Mycobacterium leprae (Leprosy, AKA Hansen’s Disease) primarily involves
involves peripheral nerves and skin in cooler regions of the body and mucus membranes and tissues of upper respiratory tract
Leprosy is the most common treatable cause of __________
neuropathy in the world
Mycobacterium leprae description
- 4 strains
- Acid-fast bacillus rod (mycolic acids in cell wall),
- Slow growth rate (estimated generation time is about 12 hours).
- Cannot be cultivated in vitro (Never cultured in vivo for diagnostic purposes)
An obligate intracellular pathogen, which grows in:
- macrophages,
2. histocytes of skin,
3. Schwann cells of nerves.
Incidence in the world most often occurs in
- Southeast Asia: India, Indonesia, Bangladesh, Myanmar (Burma).
- The remaining cases are primarily in Brazil, Nigeria
Transmission is primarily from diseased patients (esp. those with lepromatous form) via:
- aerosol route from persons with the lepromatous form of disease.
- Mucous membranes or broken skin on the one person makes direct contact with skin lesions from persons with the lepromatous form of disease.
Most common form of infection is
asymptomatic form
With respect to Schwann cells (SC) The organism binds laminin-2 to alpha-dystroglycan on Schwann cells (these binding proteins are not found in CNS) to enter Schwann cells. Only infects __________
non-myelinating SC that surrounds bundles of small diameter sensory nerve fibers.
Also causes demyelination of peripheral nerves, which activates myelin-forming SC to ___________ (this is a normal physiological process for myelin-forming SC).
de-differentiate & become non-myelinated
-These de-differentiated SC are now susceptible to infection by M. leprae
Sensory nerve loss in initially confined to
to the skin rash (with losses to temperature greater than losses to pinprick and light touch. Proprioception and vibration modalities are often preserved).
Sensory nerve loss progresses to
multiple mono-neuropathies with large nerve sensory and motor involvement and distal painless injuries.
The nerves affected are primarily the pressure/trauma-dependent nerves, with the ulnar nerve at the elbow involved most often, followed in order by
the superficial radial cutaneous and median nerve at the wrist, sural, radial, Popliteal fossa - Common peroneal nerve, Great auricular nerve in the neck and branches of the facial nerve (facial paralysis/lagophthalmos)
Deep tendon reflexes generally ________
preserved because the muscle spindles and large-fiber nerves are not involved
3 cardinal signs of disease
- Skin lesions.
- Skin anesthesia.
- Peripheral nerve enlargement
Peripheral nerve enlargement causes 3 things:
KNOW!!!
- **Deformities due to weakness and wasting of muscles (eg, claw hand or foot drop secondary to muscle weakness)
- **Sensory symptoms, such as diminished to complete loss of sensation, paresthesias in the distribution of affected nerves, and neuralgic pain when the nerve is struck or stretched.
- **Spontaneous painless blisters, burns, and trophic ulcers on hands and feet, post sensory loss
Disease Classification is based on the immune response of host
Ridley Jopling classification:
- Tuberculoid (TT) form
- Lepromatous (LL) form
- Borderline (3) forms (borderline boarderline, BB, BT, BL)
To classify, World health organization uses:
- Paucibacillary (PB) leprosy is defined as five or fewer skin lesions without detectable bacilli on skin smears = TT form.
- Patients with only a single skin lesion are classified separately as single lesion PB = TT form.
- Multibacillary (MB) leprosy is defined as six or more lesions and may be skin smear positive = LL form
Tuberculoid (TT) form, is it contagious?
NO
Tuberculoid (TT) form description
- Damage to patient’s skin and nerves occur via CMI
- Patients have a positive response to lepromin skin testing
- sensory loss in the skin rash, multiple mono-neuropathies with large nerve sensory and motor involvement
- There is no caseous necrosis observed in skin lesions but it may be present in peripheral nerves
Skin lesion description in Tuberculoid form (TT)
- *skin plaques**
- granulomatous (CMI response to agent)
- large, asymmetric, few in number
- hypopigmented, flattened, dry, scaly center.
- sharply demarcated, raised edge,
- with no sensation in center of lesion or the whole area around the lesion due to invasion of the nerves
- with few acid-fast organisms present.
- lesions tend to destroy the normal skin organs such as sweat glands and hair follicles
Skin lesions with TT are unique because
they have no sensation in center of lesion or the whole area around the lesion due to invasion of the nerves
For TT, Sensory loss as described above with progress to multiple mono-neuropathies occasionally causes ___________
extreme pain beyond endurance
Lepromatous (LL) form - Contagious, yes or no?
YES
During Lepromatous (LL) form damage to patient occurs via __________: Macrophages infiltrate the infection site with histocytes and engulf large numbers of bacilli, fill-up with lipid debris from bacilli, and enlarge, they are then designated as ___________, and cause skin lesions but multiple, __________ lesions throughout the body (nerves, eyes, and internal organs in addition to the skin).
Innate immune response
“foamy macrophages”
symmetrically distributed
