Chronic granulomatous infection caused by the bacillis, Mycobacterium leprae – affects predominantly the cooler parts of the body and is a common cause of sensory neuropathy in underdeveloped countries. Appears to be transmitted by nasorespiratory route. First described by Hansen in 1873. Rarely fatal, but can cause significant disability.
Primarily a problem of developing countries due to public health interventions in the developed countries; 5-20 million people are estimated to be affected; estimated that only half are receiving antibiotics; India has the most cases; estimated to be 6000 cases in USA; Southern Texas and Louisiana in the USA are considered endemic for leprosy.
Diagnosis of ‘leprosy’ has social consequences (stigmatised due to societal attitudes) – can be socially isolated by the community.
M. leprae most commonly affects peripheral nerves, skin and upper respiratory tract; gram positive bacillus (acid-fast, rod shaped); obligate intracellular parasite; transmitted by direct contact – contagiousness is low contact must be intimate and prolonged; portal of entry is most likely an abrasion in skin or mucous membrane; incubation of months to years.
Pathogenesis depends on presence of cell mediated immunity:
• disease only affects a few sites in the skin or peripheral nerves cell mediated immune response is effective. Lesions remain localised.
• better prognosis
Lepromatous leprosy (most cases in USA are of this type):
• no cell mediated immune response organisms widely spread widespread slowly progressive tissue damage
• nerve trunks thicken; overgrowth of connective tissue; axon and myelin sheath degenerate
• between two above groups
• all forms of leprosy may undergo an acute exacerbation
• in lepromatosus leprosy, this is due to an immune mediated vasculitis; in tuberculoid leprosy, it is due to an acute increase in cellular hypersensitivity.
Cardinal sign is sensory loss; gradual onset – first sign is usually a localised area of loss of sensation or skin macules/rash (hypopigmented and erythematous); loss of sensation is due to intracutaneous nerve damage; loss of sweating in areas of sensory loss
Tuberculoid – usually only a few asymmetrical and well localised sites; spread of infection is limited; skin lesions are usually well demarcated hypopigmented macular or raised plaques at any site on body; sensory loss mostly limited to area of skin lesion; tends to heal spontaneously with no residual problems.
Lepromatous – early skin lesions are hypopigmented macules that are erythematous – small and more widely scattered than tuberculoid lesions; sensory loss not restricted to area of skin lesion; Nerve damage is a later manifestation; nasal stiffness develops and cartilaginous septum may be perforated due to upper respiratory tract involvement; anterior eye can be involved; enlarged nerves can be palpated; paralysis develops as neuropathy progresses
Indeterminate type of leprosy – usually just the initial skin lesion may clear spontaneously or progress to tuberculoid or lepromatous types; only a small number are of this type
Lepra reactions – in tuberculoid painful tender nerves, swollen and new skin lesions. In lepromatosus tender papules that may ulcerate, painful/tender nerves, fever, lymphadenopathy
Involvement of the foot:
Neuropathy – sensory loss is initially patchy distribution (diabetic neuropathy is ‘stocking and glove’ distribution); more severe in lepromatous type puts foot at risk for trauma; muscle wasting from motor nerve involvement intrinsic muscle atrophy, clawing of toes, foot drop.
Early neuropathy – impairment of light touch, loss of temperature and pain sensation – proprioception and tendon reflexes are initially not affected; dorsal surfaces of feet affected before plantar surface
Protection of anaesthetic limbs
Antibiotics – dapsone (folate antagonist), rifampin
Social rehabilitation (education of family and community members about nature of disease and transmission)