HHTM staff: In the penultimate post on leprosy, the series finally begins addressing how the auditory/vestibular system fits into the spectrum of symptoms comprising this 20+ million year old disease. The bacterial parasite that haunts the human body and causes leprosy had evaded scientific and medical understanding, even in the modern world. Audiology is no exception.
Added to the evasive nature of the bacilli, the stigma attached to those thought to suffer from leprosy has persisted for centuries. As a result, isolation and concealment have consistently trumped systematic investigation. A successful treatment was not found until the mid 20th century and early diagnosis and vaccination remain elusive even in the 21st century.
Efforts to identify, study and treat the disease vary widely by geographic and socioeconomic regions. Published research is more common where the disease is manifest(e.g., India), but many developed countries do not systematically screen for the disease (e.g., U.S.), even though new cases appear in the hundreds every year.
Searching for Needles in Haystacks
It’s taken longer to find out less about hearing loss and leprosy than with any other infectious disease in this series so far. And no wonder: reports of leprosy-related hearing loss are few and far between, the causal nature of such hearing losses is not well established, hearing assessment methods and descriptive terminologies vary widely, and systematic studies with controls are rare.
Yet, the known effect of the disease on Schwann cells in the peripheral nervous system and the known anatomy of the Schwann cell-wrapped portion of the vestibulocochlear nerve suggest that Hansen’s disease may cause irreversible damage to the nerve, manifest as auditory and vestibular disorders.
The following summaries and hints are what could be gleaned from the inadequate literature on this topic.
Anecdotal References to Auditory Disorders in the Leprosy Literature
Amundson & Ruddle-Miyamoto (2010) comment that “hearing loss and a hoarse voice are frequent,” noting that “loss of vision and hearing…were well known” in the Moloka’i leper colony. No information is provided on prevalence or type of hearing disorders.
Schuring & Istre (1969) confirm and extend the thought:
“Throughout long history of Hansen’s disease (leprosy) the effect of the bacillus on the inner and middle ear has not been known. Since the disease affects peripheral sensory nerves, it would seem logical that the acoustic nerve, also a sensory nerve, could be involved. The upper respiratory tract also is directly involved, and secondary ear disease is a possibility. Any involvement of the inner or middle ear would cause a change in hearing.”
The same study (available only in abstract) dangles a few intoxicating hints that audiograms exist, though I have found none in print:
“Audiograms on patients with Hansen’s disease, reported by DeCandia and Marino, were interpreted as specific evidence of cochlear and acoustic nerve damage. Further evidence was cited by Sacheri, in stating that 28% of his survey had a hearing loss. Twenty-five of his patients had chronic otitis media, but the bacillus could not be found in the ear. Usmanov later claimed this hearing loss may be the result of a specific bacillus intoxication.”
Published Reports and Studies
Table 1 contains all studies of Hansen’s disease that could be found at this date, which referenced quantified measures of eighth nerve, hearing, and/or balance disorders related to the disease. It is a hodge podge table with data from some studies available only through secondary sources, abstracts only in other cases, methods and results incompletely described (for this article’s purposes) in some primary sources, and a confusing mix of qualitative and quantitative measures throughout. The table will probably improve over time as important primary sources such as the Indian Journal of Leprosy expand there online archiving efforts (IJL only goes back to 2008 at the time of writing); also, as more new research is performed.
Assumptions were made in compiling Table 1. Those studies that described findings in general terms (e.g., “impaired hearing” and “vestibular hypofunction”) were interpreted and placed in the table based on other information gleaned from the Methods sections. Some studies relied on survey data and tuning forks, rather than audiometric testing, to categorize audiovestibular status in their subjects (e.g., Singh et al., 1984). One study (Wani et al, 2009) used audiometry “to confirm sensorineural hearing loss” but stated elsewhere that audiometry was not performed.
Studies highlighted in yellow in the table are those in which audiometry and sometimes ENG/caloric tests were documented in some way as part of the methodology.
Though not shown in the table, one thing that relevant studies seem to agree on is that hearing loss is only present in patients with the lepromatous form of leprosy and not found in the more limited tuberculoid form form. (note: This series has not delved into the different forms of leprosy except to note that they exist).
Implications for Audiovestibular Disorders
Despite the paucity of data and diversity of methodologies, Table 1 suggests that vestibular disorders are uncommon or not related to Hansen’s disease.
But, Table 1 also suggests that hearing loss is under-reported in this disease, possibility to a large degree.
Finally, it suggests that sensorineural or perhaps neural hearing loss are associated with Hansen’s disease, in addition to the known effect of the disease on the external ear and middle ear disorders secondary to pharyngeal/Eustachian tube disorders associated with leprosy.
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Amundson, R & Ruddle-Miyamoto, AO. A wholesome horror: The stigmas of leprosy in 19th century Hawaii. Disability Studies quarterly, 30(3/4), 2010.
Awasthi SK et al. Audiovestibular involvement in leprosy. Indian J Lepr. 1990 Oct-Dec;62(4):429-34.
Celik, O, et al. Auditory brain stem evoked potentials in patients with leprosy. Int’l J of Leprosy, 1997, 65(2), 166-169.
Decandia, A. and Marino, A. (1960): Studies of Cochleovestibular functions in patients with leprosy. Riv Audiol Prat 1; (7–9): 135.
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Wani, A.A., et al. A clinical study of the cranial nerve involvement in leprosy. Egyptian Dermatology Online Journal, 2009, 5 (2): 3.
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