A disease that’s endemic to South America
The earliest reports of leprosy date back to approximately 600 BC.3 Known as a chronic infectious disease caused by Mycobacterium leprae, it is endemic to South America, the Indian subcontinent, and Indochina.4 Early case reports indicate that leprosy was present in North America during the 1700s.1 Other than humans, however, nine-banded armadillos in the Southern United States are the only known endemic host of M leprae.1 The many morbidities that occur in patients with leprosy include ulcers, neuropathies, eye dysfunction, and irreversible neural damage; historically, they also suffered from social seclusion.4
The classification of leprosy is based on the immune response of the host and is categorized along a spectrum.4 On one end, the tuberculoid variant is characterized by a strong cell-mediated immune response; at the other end is the lepromatous variant with a weak cell-mediated immune response.4 Borderline leprosy manifests a combination of clinical and pathologic features of both lepromatous and tuberculoid variants and, depending on the host response, may be classified as borderline lepromatous, borderline borderline, or borderline tuberculoid.2
Rule out other diseases with sensory deficits
Zeroing in on a diagnosis of leprosy requires that you consider other diseases that present with erythematous (or hypopigmented) skin lesions and/or sensory deficits.2 Sensory deficits can be seen in the following diseases:2
- diabetes mellitus
- amyloidosis
- acquired immune deficiency syndrome
- peripheral muscular atrophy
- alcoholism
- nutritional deficiency
- heavy metal poisoning
- syringomyelia
- polio.
Unlike the diseases listed above, leprosy is the only one that produces palpable peripheral nerves.2
The differential for erythematous annular lesions includes tinea corporis, mycosis fungoides, granuloma annulare, psoriasis, sarcoidosis, lichen planus, secondary syphilis, and erythema annulare centrifugum.2