The incubation period is very long, ranging from 1 to 2 yr to 40 yr. Most people who have significant exposure to M.leprae do not become diseased and often develop serum antibodies and cellular immune responses to M.leprae . Rashes as in all forms of leprosy, are nonpruritic. Peripheral nerves may be damaged and enlarged. They may lose eyelashes and eyebrows.
Patients have features of both polar forms.
Most complications or leprosy are due to peripheral nerve involvement resulting from either the infection and its resultant inflammatory response to neuritis. The ulnar nerve at the elbow is the most common trunk involved, leading to distal hypoesthesia and clawing of the 4th and 5th digits in severe cases. Plantar ulcers with secondary infection are a major cause of morbidity. The eyes may be severely affected in several ways. In LL, organisms invade the anterior chamber, ENL may cause iritis, leading to glaucoma.