Allergic Rhinitis – causes, symptoms, diagnosis, treatment, pathology


“Rhin” refers to the nose and “itis”
refers to inflammation, so rhinitis is nasal inflammation. Allergic rhinitis is also called hay fever,
because it’s typically caused by allergens like hay, as well as pollen, dust, animal
hair, or mold spores. Since the main trigger is pollinating plants,
allergic rhinitis will flare up at specific times of the year. Allergic rhinitis is a type 1 hypersensitivity
reaction, which is a type of allergic reaction that starts with exposure to an environmental
allergen. So – let’s say that a bit of pollen enters
the nose. It can get picked up by a dendritic cell which
is a type of immune cell that gobbles up foreign particles and presents it to a nearby lymphocyte
called a T cell. If that T cell gets activated, it kicks into
action, producing cytokines which helps to get other immune cells involved. The exact type of T cell determines the type
of immune response, and in allergic rhinitis there’s a bit of a T cell imbalance. There are too many T cells that, when activated,
stimulate B cells, another group of lymphocytes, to produce IgE antibodies. Those IgE antibodies get released into the
bloodstream and bind to mast cells, which are immune cells in the tissue that carry
within themselves a load histamine. Once bound by IgE the mast cells are “primed”,
meaning if pollen enters the body again in the future, those mast cells degranulate and
release their histamine into the local tissue. The histamine causes blood capillaries to
dilate and become leaky which brings more fluid and immune cells to the area where the
mast cells are located. Because the eyes and nose are portals of entry
for infections, there are lots of mast cells around those areas for extra protection. So those IgE-primed mast cells release their
histamine, which causes nearby capillaries to dilate – flooding the facial tissues with
fluid. Interestingly, there’s evidence that early
exposure to allergens might protect against type 1 hypersensitivity. For example, children who grew up on farms
and have pets at an early age typically have lower rates of allergic rhinitis. It’s thought that a combination of genetic
factors and environmental factors like these contribute to which type of T cell group is
most common and thereby influences the overall immune response. The symptoms of allergic rhinitis are related
to the excess fluid in the facial tissues. It causes nasal congestion, and red, itchy,
swollen eyes with frequent bouts of sneezing. Symptoms can begin just minutes after exposure
to allergens, and can persist for weeks at a time, affecting the ability to concentrate
and sleep, as well as attend work or school. The diagnosis of allergic rhinitis is generally
based on simply the way the skin looks, and when possible, it’s helpful to identify
the allergic trigger so that a person can avoid them in the future. One way to identify an allergic trigger is
with SKIN-PRICK test where small drops of allergens are placed on the skin and then
pricked into the skin with a tool; again, to see if there’s evidence of an allergy
like raised bumps or weals – otherwise known as itchy red skin. These tests can test for many allergens at
once, but they can sometimes have low sensitivity and low specificity. In other words, sometimes a person might have
no allergic reaction on the skin test, but have a localized allergic reaction affecting
the nasal cavity and eyes – that’s low sensitivity. Other times a person might have a skin reaction
to something, even though they don’t normally have symptoms when they encounter that allergen
in their everyday life – and that’d be low specificity. Typically, the best thing for allergic rhinitis
is to simply avoid the triggering allergen if possible. If there are symptoms, antihistamine medications
can be used to suppress the effect of mast cell degranulation. Nasal irrigation can flush out the sinuses,
reducing the congestive symptoms of allergic rhinitis. In some situations, it’s also possible to
rewire the body’s immune response to an allergen by exposing it to micro-doses and
slowly ramping up to a full dose of the allergen. This gradually boosts tolerance to the allergen
by reducing the immune system’s tendency to produce IgE each time. Alright, as a quick recap – allergic rhinitis
is a type 1 hypersensitivity reaction which results in inflammation of eyes and nose. Airborne allergens like pollen, dust, animal
hair, or mold spores cause mast cells in the tissues to release histamine, causing the
eyes and nose to get inflamed and watery. Avoiding allergens is the best approach, but
it’s also possible to use antihistamines, and in severe cases try desensitization to
reduce or eliminate the symptoms.