Pure or Primary neuritic Leprosy (PNL)

Leprosy is primarily a disease of the nerves. Mycobacterium leprae infects the Schwann cells (SC) that surround the nerve fibres and axons. Leprosy is a complex disease known for having great variability in its clinical presentation, sometimes with more nerve involvement and related anesthesia and deformities and sometimes with skin lesions primarily. In about 4–8% of the cases the clinical presentation is exclusively with nerve involvement in the form of nerve deficit or nerve thickening, without any cutaneous lesions, with a negative skin smear and no other identifiable pathology. This is commonly known as pure neuritic leprosy (PNL) and is more common in the Indian subcontinent. In India the incidence varies from 5·5 to 17·7% of all leprosy cases. The most common presentation of PNL is a mononeuritis (single nerve involvement) which occurs in about 60% of the cases. When more than one nerve is involved in an asymmetrical distribution it is known as mononeuritis multiplex, while symmetric involvement is called polyneuropathy or symmetrical polyneuritis. Nerves in the upper limbs (ulnar, radial cutaneous) are involved more often, and temperature and pain sensation are the first to be affected, but the patient may complain of sensory and/or motor impairment, numbness, parasthesiae and neural pain. – 6