Pathophysiology of allergic fungal sinusitis

Introduction:

Allergic fungal sinusitis is known to cause extensive sinonasal polyposis. This article discusses the pathophysiologic mechanisms involved. Studies have revealed that this is a form of non invasive fungal sinusitis causing sinonasal polyposis. Hypersenstivity to fungus has been implicated as the probable cause. Hypersensitivity to Aspergillus / dematiaceous fungi (this group of fungi secrete melanin in their cell walls) have been commonly implicated to the cause.

Role of hypersensitivity:

Eventhough hypersensitivity to fungus has been implicated as the cause for allergic fungal sinusitis the precise nature of this hypersensitivity is still not clear. Studies reveal that patients with allergic fungal sinusitis show elevated levels of IgE and IgG to fungal proteins. Hence a combination of Coomb's Type I and Type III hypersensitivity to these fungal allergens could play a role.

Type I hypersensitivity reaction is rather immediate and is caused by IgE and IgG4 immunoglobins.

Type III hypersensitivity reaction is known to be causeed by immune complex formation and is caused by IgG and complements.

Current hypothesis suggests that allergic fungal sinusitis develops in susceptible persons due to a combination of local anatomic as well as environmental factors. Fungi enter the nose and trigger immune response causing inflammatory changes. This inflammation induces polyp formation and accumulation of allergic mucin. Fungi which are trapped within the mucosa of nasal cavity causes continuing stimulation of immune reaction causing a vicious cycle leading on to extensive nasal polyp formation.