Welcome
Epidemiology of nasal polyp
By
Dr T Balasubramanian
Introduction:
Lot of developments have taken place in the field of epidemiology of
nasal polypi. Before dwelling into them it will be better to analyse the
conclusions of various studies in this subject. These conclusions are:
The prevalance of nasal polypi in general population is about 1-3%.
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Studies have demonstrated that the link between nasal polyp and allergic rhinitis is very weak.
Cohort studies of recent times have demonstrated a strong association between asthma and nasal polyposis
The incidence of nasal polyposis increases progressively with age. Common age group of occurence being 30 – 60 years
Nasal polpi in children should prompt investigations to rule out cystic fibrosis
Incidence of aspirin intolerance is rather high in patients with nasal polypi
Genetic predisposition to nasal polypi is rather unclear
Allergic fungal rhinosinusitis have been categorically proved to be a factor in nasal polyposis
Classification of chronic rhinosinusitis:
Chronic rhinosinusitis has been classified into:
Chronic sinusitis without nasal polypi
Chronic sinusitis with nasal polypi
Chronic rhinosinusitis without nasal polypi are commonly seen in TH1
mediated inflammation (activated T helper cells). TH1 lymphocytes
are potent inducers of inflammation. This type of inflammation is also
seen in antrochoanal polyp. Hence it is mandatory to differentiate
these two conditions. The process of differentiation is rather easy
because antrochoanal polyp has the following unique features:
They are unilateral
They present posteriorly
Chronic rhinosinusitis with nasal polypi are caused by TH2 mediated
inflammation. This type of inflammation is commonly seen in patients
with bronchial asthma.
At this juncture let us briefly review TH1 and TH2 immune responses.
TH1 and TH2 are polarized responses of body's T – helper cells when
faced with pathogens. Under normal conditions both these types of
reponses should be fully functional to enable our immune mechanism
to get rid of the pathogen. Disease begin to develop if one or the other
type of immune mechansim becomes predominant. TH2 becomes
predominant in patients with bronchial asthma and nasal polyposis
where as TH1 is predominant in patients with chronic rhinosinusitis
without nasal polypi. The T lymphocytes produce cytokines which are
responsibe for the immunological mechanism of the body. Basically
the cytokines produced fall into two categories:
Cytokines secreted by T – helper cells type I. These are inflammatory mediators and hence known as proinflammatory cytokines.
Cytokines secreted by T – helper cells type II. These inflammatory mediators are known for their anti inflammatory response. They are also know to evoke allergic response.
Co morbid conditions associated with nasal polyposis:
Allergic rhinitis
Generalized atopic status
Bronchial asthma
Role of nasal allergy in the pathogenesis of nasal polypi:
Studies have demonstrated that there is no significant increase in the
incidence of nasal polypi in patients with allergic rhinitis. Infact the
incidence of nasal polypi in this group is almost the same as that of
general population.
Role of Asthma in the pathogenesis of nasal polypi:
Studies conducted (cohart) have clearly demonstrated that the
incidence of nasal polypi is more in patients belonging to this group. It
should be borne in mind that Asthma is mediated by TH2 type of
inflammation.
Role of Atopy:
Studies have demonstrated that atopy was more prevalent in patients
with chronic rhinosinusitis without nasal polypi thus effectively ruling
out atopy as a contributing factor for nasal polyposis.
Age & its relationship to nasal polypi:
Studies have demonstrated that the incidence of nasal polypi increases
with age. The incidence reaches the peak at 50 years of age.
Asthmatics over the age of 40 are four times more prone to develop
nasal polypi than others.
Genetic predisposition:
Studies have demonstrated that nearly 15% of patients with nasal
polyposis have a positive family history. This could be taken to be a
pointer for genetic predisposition. But large cohart studies performed
have not been able to clearly pin point genetic predisposition in these
patients.
Allergic fungal rhinosinusitis:
Patients with AFRS have a strong predisoposition towards extensive
nasal polyposis. It can hence be considered as the pathophysiologic
etiological factor in some patients with nasal polyposis.
Diagnostic pointers for diagnosis of AFRS:
Type I hypersensitivity to demataceous fungi
CT scan findings – inspissated mucous secretions with calcification
Eosinophilic mucous containing charcot Leyden crystals
Positive fungal elements isolated from sinus contents
Racial differences in nasal polypi patients:
Nasal polypi due to AFRS is known to affect patients with low socio
economic status. In caucasians Nasal polypi demonstrate strong
eosinophilic component while in Asian population neutrophilic pattern
predominates. The exact reason for this variation is yet to be
elucidated.
