Leprosy classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: João André Alves Silva, M.D. [2]

Overview

The Ridley Jopling classification and the WHO classification are the two most widely used systems to classify Leprosy. These classification systems are based on clinical, microbiologic and histopathological features, and are used to determine the patient's prognosis and the treatment regimen.

Classification

Leprosy may present among different patients, or even in one single patient throughout the course of the disease, with a variety of clinical, histopathological and bacterial manifestations. Subclassification of Leprosy type determins prognosis, infectivity rate and the appropriate treatment. The two most common classifications include the WHO and the Ridley-Jopling classification.

There are several subclassification schemes for the diagnosis of Leprosy:

• The World Health Organization system distinguishes "paucibacillary" and "multibacillary" based upon the proliferation of bacteria
• The SHAY scale provides five subclassifications.
• 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, there are three sublclasses.

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)

Ridley Jopling classification

There are 5 classes in the Ridley Jopling classification scheme.

Tuberculoid or Pauci-bacillary Pole

This is the least severe form of the disease. In this form of the disease the following are present:

• 1 to 3 well-defined lesions with a central hypopigmented area, with hypoesthesia, a well-developed immune response from the patient, with evidence of an adequate granulomatous inflammation and presence of very few acid-fast bacilli; to the lepromatous or multi-bacillary pole, in which patients presents with numerous undefined nodular lesions throughout the body, with a weak immune response towards the bacteria, histological evidence of foamy macrophages in dermis filled with a great number of mycobacteria. On this last pole, it is important to notice that even though the immune system is not capable of mounting an immune response towards the bacilli, patients are still immunocompetent for other diseases. For this classification contribute the following elements:
• Cutaneous
• Neurological
• Biopsy findings
• Immunological status
• Sum of acid-fast bacilli in the dermis.

Between these two poles, there is also the intermediate, dimorphous or borderline state. This last category is subdivided into 3 subcategories, depending on the pole each subcategory has more similarities with, which include:

• Borderline Tuberculoid, or BT
• Mid-Borderline, Borderline-Borderline, or BB
• Borderline Lepromatous, or BL

This intermediate category is considered to be the one where the disease usually begins. It will then progress to one of the poles:

• In case of progression towards the tuberculoid pole, it means the patient's cell-mediated immunity is increasing, thereby being associated with inflammation of the nerves and skin.
• In case of progression towards the lepromatous pole, usually occurring before treatment is initiated and is compatible with loss of cell-mediated immunity.

Some patients show evidence of early unspecific lesions and nerve infiltrates, lacking the required criteria for being classified as above mentioned. These patients are included in a specific category called indeterminate. This category should only be used when there is diagnostic proof of leprosy, from a biopsy sample showing evidence of mycobacteria leprae and perineural infiltrates, but the disease is not advanced enough to show the clear patient position in the leprosy classification.

WHO classification

The WHO organization has defined a more simple and straightforward classification, according to the number of skin lesions present. This classification is due to be used when there is lack of laboratory support or clinical expertise, in which case, the disease will be classified as paucibacillary leprosy or multibacillary leprosy. However, despite useful in certain occasions, this method may lead to misclassification of some patients, resulting in undertreatment of some cases.

This classification allows, however, for a rapid diagnosis, selection and initiation of treatment, according to the class of leprosy:

Paucibacillary or PB

• Higher level of immunity.
• Lower number of bacilli.
• Up to five skin lesions in total body examination.
• Requires less intensive treatment - will need two instead of three antileprosy drugs, for a shorter period of time.

Multibacillary or MB

• Lower level of immunity.
• Higher number of bacilli.
• Six or more skin lesions in total body examination.
• Requires intensive treatment - will need three instead of two antileprosy drugs, for a longer period of time.

If a skin smear is done and shows a positive result, then that patient will immediately be classified as a multibacillary patient, irrespective of the number of skin lesions identified on physical examination.

References

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