Which conditions are included in the differential diagnoses of allergic fungal sinusitis (AFS)?

Updated: Apr 13, 2020
  • Author: John E McClay, MD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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A positive fungal culture does not confirm the diagnosis of allergic fungal sinusitis (AFS), nor does a negative culture exclude it. For example, fungi may proliferate as saprophytic growth in diseased sinuses. Furthermore, mycology laboratories vary in capability, and specimen handling significantly influences the rate of positive fungal cultures in a clinical setting. Allergic mucin remains the most reliable indicator of allergic fungal sinusitis (AFS). Because nasal polyposis and fungal disease in the sinuses are not unique to allergic fungal sinusitis (AFS), other mycotic diseases in the differential diagnosis must be defined and include the following:

  • Invasive fungal sinusitis: This condition typically is encountered in patients who are immunocompromised or have diabetes mellitus and is characterized by angioinvasive fungal penetration of tissue. Hypesthesia, local pain, and intranasal necrosis (in an immunocompromised person) strongly suggest invasive fungal sinusitis and help to differentiate this disease from allergic fungal sinusitis (AFS).

  • Saprophytic fungal growth: This growth may be found in one or more paranasal sinus cavities of patients who have chronic suppurative rhinosinusitis. Similar growth may occur within nasal debris of patients who have undergone aggressive sinonasal surgery or those who have rhinitis sicca. Although fungal cultures may be positive, the absence of gross and histiologic findings of allergic mucin and the lack of clinical manifestations of invasive fungal sinusitis suggest saprophytic fungal growth.

  • Mycetoma, aspergilloma, or fungus ball of the sinuses: This clinical entity differs from allergic fungal sinusitis (AFS) in presentation. Rather than involving multiple sinuses, a fungus ball typically involves a single sinus, most often the maxillary antrum or sphenoid. Patients affected by this condition are not necessarily allergic and generally do not exhibit nasal polyps. On histologic examination, the material removed from the sinuses demonstrates only fungal hyphae without eosinophils. Surgery in such patients generally is curative.

  • Eosinophilic mucin sinusitis: Pansinusitis, polyposis, and mucin that is clinically indistinguishable from that of allergic fungal sinusitis (AFS) are characteristic. However, examination of mucin reveals no fungal hyphae. Allergy is not as constant a feature in this condition as it is in allergic fungal sinusitis (AFS), but asthma is observed more frequently. Ferguson has suggested that this condition may represent a variant of the Samter triad.

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