Figure 142.1 Lepromatous leprosy on the ear.
The World Health Organization (WHO) schema is the most commonly used classification system and is based on the number of skin lesions and number of bacilli present in smears. Patients with five or fewer skin lesions without evidence of bacilli on skin smears are considered paucibacillary, whereas those with six or more skin lesions with or without bacilli on skin smears are considered to be multibacillary. Classification of patients into multibacillary and paucibacillary groups determines the duration of their treatment.
Leprosy in reaction refers to clinical disease produced when there is a change in the host’s immune response to M. leprae. There are two forms of reactional leprosy. Type 1 reactions are induced by cell-mediated immunity and are referred to as upgrading and downgrading reactions. Upgrading reactions are characteristically seen in patients with borderline lepromatous disease who undergo a shift toward more tuberculoid (paucibacillary) forms. These may develop after induction of therapy. Downgrading reactions occur with transformation from a tuberculoid to a more lepromatous (multibacillary) form and often develop in the absence of treatment. Both may appear similar clinically and are manifest by erythema and edema of existing skin lesions associated with painful neuropathy and ulceration.
Type 2 reactions are immune complex mediated and include erythema nodosum leprosum (ENL) and Lucio’s phenomenon. Both of these are manifestations of immune complex-mediated vasculitis that lead to prominent inflammation and often ulceration with acute damage to nerves. Patients present with fever; multiple erythematous tender nodules; and varying degrees of neuritis, edema, arthralgias, leukocytosis, iridocyclitis, pretibial periostitis, orchitis, and nephritis.
Patients infected with human immunodeficiency virus (HIV) do not have an increased incidence of leprosy, and coinfection with M. leprae and HIV appears to have minimal effect on the course of either leprosy or HIV.
Diagnosis
The diagnosis is primarily clinical and is based on the presence of one of three cardinal findings: hypopigmented or reddish patches with definitive loss of sensation, thickened peripheral nerves, and demonstration of acid-fast bacilli.
Definitive diagnosis of M. leprae is difficult, as the organism cannot be cultured in vitro. The gold standard for the diagnosis of leprosy is a skin biopsy specimen obtained from the advancing edge of an active lesion and detection of bacilli in tissue sections using the Fite–Faraco staining method. The slit skin smear has a high specificity but a low sensitivity (10%–50% of all leprosy patients are smear negative). Slit skin smears may be useful as an adjunctive procedure to semiquantitate acid-fast organisms in infected skin for monitoring the response of patients during and after treatment.
Serologic tests have been developed to detect IgM antibodies to phenolic glycolipid I (PGL-I), a glycolipid unique to M. leprae. The sensitivity of these tests depends on the type of leprosy, and these tests are most useful in distinguishing those individuals with lepromatous leprosy from those with paucibacillary or tuberculoid leprosy after diagnosis. Although individuals positive for PGL-I have approximately an 8-fold risk for developing clinically apparent leprosy, it is not a useful screening test in the general population, as a positive test does not necessarily predict development of the disease.
Another major recent advance in the laboratory diagnosis of leprosy is the development of PCR assays that have reported specificity of 100% and a sensitivity ranging from 34% to 80% in patients with paucibacillary forms of the disease to greater than 90% in patients with multibacillary forms of the disease.
Treatment
Related posts:
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
