Clinical manifestations, diagnosis and classification of leprosy

Mycobacterium leprae, the causative organism of leprosy is slow-growing and the reason is its long incubation period of 2-4 years. Males are predominantly affected and deformity is produced in less than 2% of people affected with the disease. The disease manifests in the skin as macules, papules, nodules, plaques or infiltration. Hypopigmented or erythematous skin patches with definite sensory deficit is one of the clinical cardinal signs by which one can make a definite diagnosis. Demonstration of bacilli in the slit skin smear is the bacteriological cardinal sign used to make definite diagnosis of leprosy. Involvement of common cutaneous nerves with thickening and/or tenderness with its dysfunction is the second clinical cardinal sign used to diagnose leprosy. Diagnosis can be made by eliciting definite sensory deficit in the skin lesions (other than nodules and infiltration). In the absence of two clinical cardinal signs and when there is a strong suspicion of leprosy, slit skin smear should be taken from both ear lobes and one of the lesions for demonstration of acid-test bacilli. Clinical classification is based on characteristics like number of lesions, their margin, sensory deficit, satellite lesions, symmetry of lesions, central healing and scaling. Up to 5 lesions are grouped under paucibacillary and six and more are grouped under multibacillary leprosy.