Leprosy is caused by an infection with Mycobacterium leprae. The mode of transmission is usually not apparent.
The clinical signs and symptoms depend to a great extent on the host immune response to M. leprae.
Leprosy is classified on a continuum from tuberculoid, with a good host response to lepromatous, with a poor host immune response.
- Patients with tuberculoid leprosy usually have fewer than 10 skin lesions, asymmetrically distributed.
- M. leprae is rare in lesions and specialized histologic examination using, for instance, the polymerase chain reaction to mycobacterium antigen, may be necessary.
- Lesions are often anesthetic, with loss of autonomic function over the lesion being an early feature.
- Early neurologic findings include impairment in temperature perception.
- Lesions are sharply demarcated, red to purple plaques with a gradual slope toward a hypomelanotic center. Thickened nerves may be palpable in the vicinity of the lesion. Hair loss is common in lesions.
- Patients can have hundreds of skin lesions.
- These lesions, teeming with organisms, are ill defined. Often symmetrical, there can be extensive infiltration of the skin. Macules, papules, plaques and nodules can be present.
- Anesthesia is usually a late development and can be widespread. Autonomic dysfunction is usually mild.
- Common symptoms include nasal stuffiness and discharge, as well as extremity edema secondary to lymphatic obstruction.
- There can be extensive oral involvement with eventual perforation of the palate.
- Left untreated, skin and other lesions progress with very significant damage to the affected tissue.
- Nephritis is common.
- The Lucio variant of lepromatous leprosy, from central America, shows a diffuse infiltration of the skin that resembles scleroderma.
- Telangiectasia are common, as is alopecia.
- Most patients fit between the polar tuberculoid and lepromatous groups. In the middle are those with borderline leprosy.
- Skin lesions are often a mix of morphologies from the polar groups. Plaques may have a sloping, ill-defined advancing edge and a sharp inner edge; the morphologic "opposite" of the plaques of tuberculoid leprosy.
- Patients commonly shift toward one of the poles, spontaneously or secondary to treatment. Shifting towards the tuberculoid pole is called upgrading, with downgrading being a shift to the lepromatous pole.
- Monotherapy with dapsone is no longer recommended.
- Although there are various treatment protocols in use, patients at the tuberculoid paucibacillary end of the spectrum, in general, are given 6 to 12 months of treatment with dapsone 100 mg daily and rifampin 600 mg once monthly.
- Those at the lepromatous multibacillary end require at least 24 months of treatment with dapsone 100 mg daily, rifampin 600 mg monthly and clofazimine 300 mg monthly and 50 mg daily.
- Treatment is continued beyond 24 months if the slit smear is positive, and is continued until it is negative.
Reactions are common during the course of untreated leprosy. They can also be induced by treatment.Lepra reaction Type 1:
- Commonly associated with an upgrading reaction during treatment, Type 1 reactions often present as a neuropathy associated with pain or loss of nerve functions. Previously unrecognized lesions can appear and known lesions can become edematous and painful.
- A vasculitis most commonly associated with lepromatous leprosy, crops of painful red nodules, erythema nodosum leprosum, develop on the face and extensor surfaces, sometimes with suppuration. Fever and evidence of vasculitis in many organ systems can develop.
- Occurring in patients with the Lucio variant of lepromatous leprosy, this vasculitic process can produce generalized nodules, bullae, and ulcers. The reaction can be fatal.
Treatment of reactions:
- A type 1 lepra reaction requires aggressive treatment with systemic glucocorticoids, such as prednisone 50-100 mg daily, to prevent permanent nerve damage.
- Type 2 lepra reactions respond well to prednisone or to thalidomide 400 mg daily (in the male or non-pregnant female).
- Clofazimine, increased to 300 mg daily, also has an anti-inflammatory effect.