The unique tropism of M. leprae for peripheral nerves from large nerve trunks to microscopic dermal nerves and certain immunologically mediated reactional states are the major causes of morbidity in leprosy.
Today, with early diagnosis and the institution of appropriate and effective antimicrobial therapy, patients can lead productive lives in the community, and deformities and other visible manifestations can largely be prevented.
M. leprae is an obligate intracellular bacillus that is confined to humans, armadillos in certain locales, and sphagnum moss.
The organism is acid-fast, indistinguishable microscopically from other mycobacteria .
M. leprae grows best in cooler tissues the skin, peripheral nerves, anterior chamber of the eye, upper respiratory tract, and testes, sparing warmer areas of the skin the axilla, groin, scalp, and midline of the back.
The global prevalence of leprosy is difficult to assess. Estimates range from 0.6 to 8 million affected individuals.
Leprosy is associated with poverty and rural residence. It appears not to be associated with AIDS, perhaps because of leprosy’s long incubation period.
The route of transmission of leprosy remains uncertain, and transmission routes may in fact be multiple.
Nasal droplet infection, contact with infected soil, and even insect vectors have been considered the prime candidates.
Lepra reactions comprise several common immunologically mediated inflammatory states that cause considerable morbidity.
. Type 1 Lepra Reactions
Type 1 lepra reactions occur in almost half of patients with borderline forms of leprosy but not in patients with pure lepromatous disease. Manifestations include classic signs of inflammation within previously involved macules, papules, and plaques and fever. The nerve trunk most commonly involved in this process is the ulnar nerve at the elbow, which may be painful and exquisitely tender.
Type 2 Lepra Reactions: Erythema Nodosum Leprosum
Erythema nodosum leprosum occurs exclusively in patients near the lepromatous end of the leprosy spectrum affecting nearly 50% of this group.
The most common features of ENL are crops of painful erythematous papules that resolve spontaneously in a few days to a week but may recur; malaise; and fever that can be profound.
However, patients may also experience symptoms of neuritis, lymphadenitis, uveitis, orchitis, and glomerulonephritis and may develop anemia, leukocytosis, and abnormal liver function tests .
Complications of the extremities in leprosy patients are primarily a consequence of neuropathy leading to insensitivity and myopathy.
Insensitivity affects fine touch, pain, and heat receptors but generally spares position and vibration appreciation.
The most commonly affected nerve trunk is the ulnar nerve at the elbow, whose involvement results in clawing of the fourth and fifth fingers, loss of dorsal interosseous musculature in the affected hand, and loss of sensation in these distributions.
Median nerve involvement in leprosy impairs thumb opposition and grasp; radial nerve dysfunction, although rare in leprosy, leads to wristdrop.
In lepromatous leprosy, bacillary invasion of the nasal mucosa can result in chronic nasal congestion and epistaxis .
Long-untreated LL leprosy may further result in destruction of the nasal cartilage, with consequent saddle-nose deformity or anosmia
Owing to cranial nerve palsies, lagophthalmos and corneal insensitivity may complicate leprosy, resulting in trauma, secondary infection, and corneal ulcerations and opacities.
M. leprae invades the testes, while ENL may cause orchitis, severe testicular dysfunction, with an elevation of luteinizing and follicle-stimulating hormones, decreased testosterone, and aspermia or hypospermia
Secondary amyloidosis is a complication of LL leprosy and ENL that is encountered infrequently in the antibiotic era. This complication may result in abnormalities of hepatic and particularly renal function.
Patients with various forms of leprosy, but particularly those with the BT form, may develop abscesses of nerves with an adjacent cellulitic appearance of the skin.
Leprosy most commonly presents with both characteristic skin lesions and skin histopathology.
The diagnosis should be confirmed by histopathology.
Biopsies of normal-appearing skin are also generally diagnostic.
Tuberculoid lesions may not
(1) appear typical
(2) be hypesthetic
(3) contain granulomas but only nonspecific lymphocytic infiltrates.
IgM antibodies to PGL-1 are found in 95% of untreated lepromatous leprosy patients
Various other disorders causing hypo pigmentation (pityriasis alba, tinea, and vitiligo).