A university professor would like to conduct a study to investigate the causes of Castleman disease, a disease involving enlarged lymph nodes in the body.

Which is the most appropriate study design he should select?

Options:
explanation: This describes a prospective cohort study, a longitudinal study that observes participants over a period of time to see whether they develop the outcome in question. This would not be suitable in this case as the disease is very rare, and the time taken to develop the condition may be very long
name: A study involving two groups of patients, one infected with human immunodeficiency virus (HIV) and the other without. The groups are then followed up over a period of 5 years to determine whether or not they develop Castleman disease
label: b
answer: no
explanation: This is a retrospective cohort study, which is useful for tracking the development of a disease with a long latency period. It is different from a prospective cohort study in that study groups are not followed up in the future. It would not be suitable in this case as the disease is very rare
name: A study involving previously collected data to investigate whether there was an association between patients infected with human immunodeficiency virus (HIV) and their development of Castleman disease over a five year period
label: d
answer: no
explanation: This describes a case-control study, which is a retrospective observational study. It is best suited to study rare diseases for which the population size is very small, and would be able to look at a wide range of exposure factors from the patients' histories
name: A study involving two groups of patients, one with and one without Castleman disease. The groups are then compared to examine their exposure to possible causal factors such as human immunodeficiency virus (HIV) and human herpesvirus 8 (HHV-8)
label: a
answer: yes
explanation: This is a cross-sectional study that provides a snapshot of the disease prevalence and its risk factors in a specific population at one point in time. It would not be suitable in investigating rare diseases as it would be difficult to find a large enough sample size. In addition, it would only be able to identify a potential association between HHV-8 and Castleman disease, but would not be able to define a direct cause and effect relationship
name: A study looking at the prevalence of Castleman disease in all males aged 20-50 years old in London and finding out whether they have been exposed to human herpesvirus 8 (HHV-8)
label: c
answer: no
explanation: This is a case report, which involves an in-depth study of one to a few individuals with the disease. It is typically used to analyse unusual presentations of disease or unexpected responses to treatment, and is useful with respect to rare or emerging diseases. However, as the sample size is very limited, it would not provide as much data on the various causes of the disease compared to a case-control study
name: A study involving a patient diagnosed with Castleman disease in the university hospital, and an in-depth investigation into his possible predisposing factors to the disease
label: e
answer: no

Correct answer: a


Learning point: A case-control study, a type of retrospective observational study, is ideal for studying rare diseases or outcomes with a small population size. It allows researchers to examine a wide range of exposure factors from patients' histories to identify potential associations between exposures and the disease.