Letter to the Editor: Demonstrating Neurologic Research Disparities in the Himalayas Through Literature Review

Dear Editor,

Rural areas are known for accessibility issues and having limited health care resources. This is especially true for the Himalayas, a mountain range spanning five countries such as India, Bhutan, Pakistan, China, and Nepal. Patients in this region receive minimal medical care, and rarely have access to a neurologist. There are studies examining the neurologic disease burden of specific populations based on geographic location, genetic, or ethnocultural identity (Korczyn, 1994; Hirtz et al., 2007; Gordon et al., 2013; The Global Burden of Diseases, Injuries, and Risk Factors [GBD] Study 2015 Neurological Disorders Collaborator Group, 2015). However, little neurologic research is aimed at people living in the Himalayas (Bhandari et al., 2017; Bruno et al., 2014; Calderón-Gerstein et al., 2017).

I conducted PubMed literature searches using the medical subject heading (MeSH) search terms Himalayas, Sherpa, and Tibetan paired with MeSH search terms for neurologic conditions and conditions that affect people who experience altitude-related medical issues. Search results generated from common neurologic conditions (e.g., Himalayas AND stroke, Sherpa AND epilepsy, Tibetan AND dementia) were reviewed for their relevance to the field of neurology and whether Himalayan patients were included. Given that no one set definition of Himalayan descent exists, it was decided that content must specifically mention “Himalayan” patients or the patients' altitude was at or >2,000 m. This altitude was based on the studies by Dr. Mandahar and his colleagues. They were documenting the prevalence, clinical presentation, and burden of headache disorders in Nepalese patients at various altitudes. Patients at 2,000 m were one of the altitude groups they identified when they analyzed their data (Manandhar et al., 2015, 2016; Linde et al., 2017). A lower altitude would include urbanized areas (e.g., Kathmandu's altitude is 1,400 m).

This initial literature review reveals disproportionately more research on medical conditions that predominantly affect tourists more often. Twice as many articles were related to high-altitude conditions that are not commonly seen in the indigenous population compared with those focused on neurologic conditions within that region. The MeSH phrase pair Tibetan AND altitude sickness was the most robust search query, generating 119 unique articles, whereas there were only 23 results in for the most robust search query when searching for common neurologic conditions.

Of the search results for common neurologic conditions, only 61 (34.3%) pertained to neurology. As an example, when looking at the search results for Himalayas AND stroke, only two of seven articles were relevant. This was also seen when reviewing the search query Sherpa AND multiple sclerosis; only one of the three articles was directly relevant and it was only included because the cell phone application they were addressing in the article is owned by the company “Orikami/MS sherpa BV.” Of the remaining five articles generated when searching Himalayas AND stroke, two focused on cardiology and three focused on species of geese.

The MeSH phrase pair Himalayas AND migraine generated the most results for neurologic conditions, with 45 articles. Of those, seven were relevant and three specifically included high-altitude Nepalese patients. These three studies were by the same authors using the same data set (Manandhar et al., 2015, 2016; Linde et al., 2017), so patients were only counted once. This preliminary analysis revealed that only 22% of patients in the studies that resulted from the MeSH terms Himalayas with common neurologic ailments could be described as Himalayan.

This literature review is not comprehensive; only articles contained on PubMed were included. If future studies are done, it may be interesting to see the results when accounting for this.

The Himalayas are culturally diverse and a popular vacation destination in South Asia. The GBD Neurology group reports that South Asia had more disability adjusted life years for neurologic conditions than North America and Western Europe, and about as many as the rest of Asia with stroke and migraine contributing the most. Linde and Mandahar's studies indicate that migraine prevalence in Nepal increases with altitude, which suggests inhabitants of the Himalayas may have a different neurologic disease burden for migraine. Their work also demonstrates that obtaining robust sample sizes at high altitude is feasible. Unfortunately, there is a dearth of research indexed on PubMed when it comes to evaluating common neurologic illnesses in the Himalayas. It appears to be disproportionately focused on ailments of high altitude that are more often experienced by tourists.

Further investigation could identify opportunities to study common neurologic illnesses in the Himalayas. Aspects of these conditions unique to this region may be identified and allow those with a fiduciary duty to the people of the Himalayas to make impactful investments to improve neurologic care.