Pitfalls in the diagnosis of leprous neuropathy: Lessons learnt from a University hospital in an endemic zone

Abstract

Leprosy is the oldest disease known to mankind and has piqued humans since Before Christian Era (BCE) [1]. The causative agent, Mycobacterium leprae, was thefirst bacterium to be identified as causing disease in humans. Effective treatment, viz, Promin, was introduced only in the 1940s. Multi-drug therapy came into vogue in the 1970s [2,3] and was popularised by the World Health Organisation (WHO) in the 1980s. This resulted in a rapid decline in the new case detection rates [4]. Global efforts to eliminate leprosy have met with only partial success and the disease continues to prevail in certain endemic pockets in the developing countries [5–8]. In India the prevalence of leprosy reduced from 58 per 10,000 population in 1980 to 0.69 per 10,000 in 2010 [9]. Thus, leprosy has been ‘eliminated’ as a public health problem.However, this has not ensured complete interruption of disease transmission and new cases continue to occur, sometimes after several years because of the long incubation period. This underscores the need for active and continued efforts to identify new cases [9]. The primary targets of M. leprae are the skin and peripheral nerves [6]. The diagnosis of leprosy rests on the demonstration of one or more of the three cardinal signs namely anaesthetic/hypoesthetic skin patches, thickened peripheral nerves with impaired sensation in the areas innervated by the affected nerves and acid-fast bacilli in skin smear [4,10]. Characteristically, the superficial and cooler regions of the body are affected [11,12]. The commonly affected nerves in leprosy include ulnar, radial, median, lateral popliteal, tibial, facial and trigeminal [13]. Leprous neuropathy can occur in the absence of skin lesions [14]. Even in the presence of skin lesions, a mismatch in the severity of disease in the nerves vis-a-vis skin occurs. Thus the disease may be paucibacillary in the skin, but multibacillary in the nerves [15,16]. Untreated or delayed treatment of peripheral neuropathy is the major cause of disability, deformity, morbidity and social isolation in patients with leprosy [11]. Thus it is imperative to recognise and establish an early diagnosis and institute timely therapy. Meanwhile, each one of the cardinal signs is considered to be highly sensitive and specific for leprosy [4,10]. A considerable skill and experience is required for detecting their presence failing which the diagnosis is delayed or missed [17].