Leprosy - Classification

Classification

There are several different approaches for classifying leprosy; however, parallels exist.

The World Health Organization system distinguishes "paucibacillary" and "multibacillary" based upon the proliferation of bacteria ("pauci-" refers to a low quantity.)
The SHAY scale provides five gradations.
The ICD-10, though developed by the WHO, uses Ridley-Jopling and not the WHO system. It also adds an indeterminate ("I") entry.
In MeSH, three groupings are used.

WHO	Ridley-Jopling	ICD-10	MeSH	Description	Lepromin test	Immune target
Paucibacillary	tuberculoid ("TT"), borderline tuberculoid ("BT")	A30.1, A30.2	Tuberculoid	It is characterized by one or more hypopigmented skin macules and anaesthetic patches, where skin sensations are lost because of damaged peripheral nerves that have been attacked by the human host's immune cells.	Positive	bacillus (Th1)
Multibacillary	midborderline or borderline ("BB")	A30.3	Borderline	Borderline leprosy is of intermediate severity and is the most common form. Skin lesions resemble tuberculoid leprosy but are more numerous and irregular; large patches may affect a whole limb, and peripheral nerve involvement with weakness and loss of sensation is common. This type is unstable and may become more like lepromatous leprosy or may undergo a reversal reaction, becoming more like the tuberculoid form.
Multibacillary	borderline lepromatous ("BL"), and lepromatous ("LL")	A30.4, A30.5	Lepromatous	It is associated with symmetric skin lesions, nodules, plaques, thickened dermis, and frequent involvement of the nasal mucosa resulting in nasal congestion and epistaxis (nose bleeds), but, typically, detectable nerve damage is late.	Negative	plasmid inside bacillus (Th2)

There is a difference in immune response to the tuberculoid and lepromatous forms.

Hansen's disease may also be divided into the following types:

This disease may also occur with only neural involvement, without skin lesions. This disease is also known as Hansen's Disease.