These reactions occur in almost half of
patients with borderline forms of leprosy but not in patients with polar
disease. Manifestations include classic signs of inflammation within previously
involved macules, papules, and plaques and, on occasion, the appearance of new
skin lesions, neuritis, and (less commonly) fever—generally low-grade. The
nerve trunk most commonly involved in this process is the ulnar nerve at the
elbow, which may be painful and exquisitely tender. If patients with affected
nerves are not treated promptly with glucocorticoids, irreversible nerve damage
may result in as little as 24 h. The most dramatic manifestation is footdrop,
which occurs when the peroneal nerve is involved.
When type 1 lepra reactions precede the
initiation of appropriate antimicrobial therapy, they are termed downgrading reactions, and the case becomes histologically more lepromatous; when they
occur after the initiation of therapy, they are termed reversal reactions, and the case becomes more tuberculoid. Reversal reactions often
occur in the first months or years after the initiation of therapy but may also
develop several years thereafter.
Edema is the most characteristic microscopic
feature of type 1 lepra lesions, whose diagnosis is primarily clinical.
Reversal reactions are typified by a TH1 cytokine profile, with an influx of
CD4+
helper cells and increased levels of IFN-γand IL-2. In addition, type 1 reactions are associated with large
numbers of T cells bearing γ/ ɚ receptors—a
unique feature of leprosy.
Source:
Harrison_s_Principles_of_Internal_Medicine_16th_Edition
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