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CORRESPONDENCE
Year : 2014  |  Volume : 62  |  Issue : 3  |  Page : 343--344

Central nervous system lymphoma: Patterns of incidence in Indian population and effect of steroids on stereotactic biopsy yield

Sunil Kumar Raina 
 Department of Community Medicine, Rajendra Prasad Government Medical College, Tanda, Kangra, Himachal Pradesh, India

Correspondence Address:
Sunil Kumar Raina
Department of Community Medicine, Rajendra Prasad Government Medical College, Tanda, Kangra, Himachal Pradesh
India




How to cite this article:
Raina SK. Central nervous system lymphoma: Patterns of incidence in Indian population and effect of steroids on stereotactic biopsy yield.Neurol India 2014;62:343-344


How to cite this URL:
Raina SK. Central nervous system lymphoma: Patterns of incidence in Indian population and effect of steroids on stereotactic biopsy yield. Neurol India [serial online] 2014 [cited 2021 Mar 4 ];62:343-344
Available from: https://www.neurologyindia.com/text.asp?2014/62/3/343/137033


Full Text

Sir,

This is with reference to the article entitled central nervous system lymphoma: Patterns of incidence in Indian population and effect of steroids on stereotactic biopsy yield published in Neurology India by Manoj et al. [1] The authors need to be appreciated for their effort.

However, I have some concerns. The authors report that a retrospective review of case records was analyzed to arrive at hospital-based incidence of primary central nervous system lymphoma (PCNSL) over two decades (1991-2010), relation to immune status and effect of steroids on yield of stereotactic biopsy (STB). A review of hospital-based records is not adequate to provide us with the incidence (as mentioned by the authors). What it does provide us with is a profile of prevalence. In comparison to incidence, prevalence is the proportion of cases in the population at a given time rather than rate of occurrence of new cases. The incidence is basically a "rate" and is the number of new cases per population at risk in a given time period. [2] Furthermore, if the denominator is the sum of the person-time of the at risk population, it is also known as the "incidence density rate" or "person-time incidence rate". [3] This point is further highlighted in the results section of the article. [1] The authors write that 76 cases of PCNSL were diagnosed over a period of two decades. They further write that incidence of lymphomas amongst all biopsied lesions showed a gradual increase from 0.18% at the beginning of study period to 0.41% at the end of study period. [1]

As already detailed above, incidence is not expressed as percentages (which usual reflect proportion and therefore prevalence). Incidence encompasses frequency, so reference to time is important, and that is why, incidence is not expressed as percentages but as person-time.

References

1Manoj N, Arivazhagan A, Mahadevan A, Bhat DI, Arvinda HR, Devi BI, et al. Central nervous system lymphoma: Patterns of incidence in Indian population and effect of steroids on stereotactic biopsy yield. Neurol India 2014;62:19-25.
2Rothman KJ, Greenland S, Lash TL. Modern Epidemiology. 3 rd ed. Philadelphia, PA: Lippincott, Williams and Wilkins. 2008.
3Last JM, editor. A Dictionary of Epidemiology. 2001. 4 th ed. New York: Oxford University Press.