26
Dec
2018
F
Cr
Feature Review
Clinical
and which could be included in an exhaustive
list of differential diagnoses. Many of these
conditions are rare.
With the ready availability of over-
the-counter nasal decongestants, an
important differential to consider is rhinitis
medicamentosa (rebound/chemical rhinitis).
Non-allergic rhinitis and sinusitis complete
the list of important differential diagnoses to
consider at a patient’s initial assessment. Table 2. Some of the causes of non-allergic rhinitis
Non-allergic rhinitis
A number of the important and less rare
non-allergic causes of rhinitis are listed in
table 2; this list is not exhaustive. A systematic
approach to their consideration (in line with the
categories in the table) will save valuable time.
Sinusitis
Patients with acute sinusitis may present with
some of the features of allergic rhinitis. Age
of onset should be taken into account and this
alone may favour sinusitis. Acute sinusitis is
often accompanied by the characteristic facial
pain/pressure sensation and discoloured nasal
discharge. Hyposmia/anosmia favours the
diagnosis. The investigation and management
of sinusitis is not discussed here. However, it is
important to note that many of the agents used
in the management of allergic rhinitis will be of
benefit to patients with sinusitis.
Viral rhinosinusitis
Viral rhinosinusitis may present with very
similar symptoms to allergic rhinitis. However,
the duration of symptoms is often less than two
weeks and this condition is associated with the
systemic features of viral illness (such as fever
and myalgia).
Investigation
Therapeutic trial
A trial of intranasal and/or oral medications
is a reasonable and pragmatic step that serves
both a diagnostic and therapeutic function.
Where allergic rhinitis is the most likely
diagnosis based on history and physical
examination, and other concerning diagnoses
have been excluded, appropriate medications
can be started and the response to treatment
assessed after one month.
Laboratory studies
Skin-prick testing
Properly performed skin-prick testing is the
gold standard in the diagnosis of allergic
rhinitis. A positive skin prick test implies
first, the presence of antibodies to a given
allergen and next, an immune response to
antigen challenge, diagnostic of atopy. Skin-
prick testing is relatively easily performed in
the outpatient setting and can be used from
infancy to advanced age.
Category Condition
Mechanical Septal deviation
Adenoid/turbinate hypertrophy
Foreign bodies
Choanal atresia
Neoplastic Nasopharyngeal tumour
Infectious Rhinosinusitis
Immunologic/inflammatory Nasal polyposis
Granulomatous diseases
Sjögren’s syndrome
Medication-induced Rhinitis medicamentosa
NSAIDs/aspirin
Antihypertensives
Cocaine-sniffing
Physiological Disorders associated with ciliary dyskinesia
(cystic fibrosis, primary ciliary dyskinesia)
Hormonal Hypothyroidism
Pregnancy
Oral contraceptives
Exercise-induced
Idiopathic Vasomotor rhinitis
Pre-test considerations
Several conditions (widespread eczema,
urticaria, spinal cord injury and other
neurological conditions) and medications
(particularly oral antihistamines, imipramine,
clonidine and phenothiazines) affect the
diagnostic utility of skin-prick testing.
A comprehensive practitioner’s manual
is produced by the Australasian Society of
Clinical Immunology and Allergy (ASCIA)
that details pre-test considerations, discusses
causes of false-negative and false-positive
results, and describes the protocols of skin
prick testing.
Interpretation
Interpretation of skin-prick test results
must be made in the context of the patient’s
history, examination and clinical disease.
A positive skin-prick test to aeroallergens
with a consistent history and examination is
diagnostic of allergic rhinitis. In interpreting
test results both in the laboratory and in the
rooms, the causes of false-positive and false-
negative results should be considered.
Other allergen challenge testing
Other allergen challenge tests (patch test,
intradermal allergen challenge, scratch tests)
are not routinely used to diagnose
allergic rhinitis.
RAST
The radioallergosorbent test (RAST)
measures serum-specific IgE against
antigens. Its reliability is likewise affected by
the quality of the allergens used.
The positive predictive value of serum-
specific IgE is more than 85%. 8 This
investigation will determine whether a
patient has IgE against a specific agent, but
this does not necessarily equate with clinical
disease, and must be interpreted in light of
the patient’s history and examination.
IgE quantification
Serum-total IgE is elevated in parasitic and
other allergic diseases, and this investigation
plays no role in the routine investigation of
isolated allergic rhinitis.
Mucosal challenge
At present, direct nasal mucosal challenge is
used exclusively in clinical trials and not as
an investigative tool in clinical practice.
References on request. This is an unedited extract
from the original article that appeared in Australian
Doctor. See full article online: HowToTreat.com.au
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