Nasal Myiasis Mimicking Allergic Rhinitis : A Report of 14 Adult Cases

3.4. Complementary Examinations and Parasite Identification

Allergic skin prick tests performed on all patients were negative, thus excluding an underlying allergic rhinitis diagnosis. Facial computed tomography (CT) scans were performed in five patients (36%) and revealed no structural abnormalities or signs of infestation extension.

Parasitological examination of the extracted larvae allowed for the identification of Oestrus ovis in 10 cases (71%).

Macroscopic and microscopic examination of the larvae enabled us to identify the species Oestrus ovis according to Zumpt’s criteria. They were L2 stage larvae (between 5 and 6 mm in size) (Figure 1 and Figure 2). The larvae are semi-cylindrical in shape. The posterior respiratory stigmata are subcircular with a central knob and pierced by numerous pores (Figure 3).The pseudocephalon has two buccal hooks (Figure 4).

In four cases, the identification was not possible.

4.1. The Mimicry of Allergic Rhinitis: A Diagnostic Challenge

The initial symptoms reported by our patients: intense nasal pruritus, sneezing, sudden onset, nasal obstruction, rhinorrhea and headache, are very consistent with those of acute allergic rhinitis. This symptomatic overlap, combined with the rarity of nasal myiasis, probably contributed to the average 6-day delay in diagnosis and ineffective initial treatment with antihistamines and local corticosteroids. Although allergic rhinitis is a common diagnosis worldwide, our findings highlight the need for a higher level of suspicion when such “allergic” symptoms are atypical or refractory to standard treatment.

The literature confirms this diagnostic dilemma. Many case reports describe nasal myiasis presenting with non-specific rhinitis-like symptoms, such as nasal discharge, congestion and irritation, leading to an initial misdiagnosis of sinusitis, common cold or even a foreign body [4]. The sensation of something moving in the nose, severe pain, or epistaxis are often described as “red flags” that eventually differentiate myiasis [5]. In our series, the spontaneous expulsion of a larva by a patient during a sneeze was a spectacular and immediate clue, which meant that the diagnosis was not further delayed.

4.2. Clinical Clues and Diagnostic Modalities

Our study highlights that, while initial symptoms may mimic allergic rhinitis, certain features should prompt further investigation. The sudden onset of severe symptoms, the lack of response to conventional anti-allergic treatments and the possible presence of mucopurulent secretions were consistent findings. Although otalgia, observed in three of our cases, is not a typical symptom of allergic rhinitis, it is a known though less frequent manifestation of myiasis, perhaps due to larval migration or inflammatory extension.

The crucial role of nasal endoscopy cannot be overestimated. In all our cases, endoscopy immediately revealed the characteristic whitish, motile larvae, even when the initially suspected symptoms were mild. This is in line with current recommendations, which call for a rapid endoscopic examination of any patient presenting with atypical or persistent nasal symptoms, particularly in the presence of predisposing factors or in the event of failure of initial treatments [6]. Negative allergological skin tests in all our patients reinforced the exclusion of allergic rhinitis and confirmed the parasitic etiology.

Also of interest were the results of facial CT scans, which were normal in all five patients in whom they were performed. This suggests that in the early stages, or in cases of Oestrus ovis infestation (which generally remains superficial unless complicated), significant bone erosion or deep tissue invasion may not be immediately apparent. This reinforces the primacy of direct visualization by endoscopy for diagnosis.

4.3. Epidemiology and Predisposing Factors

Our series, with 43% of patients originating from rural areas, aligns with the known epidemiology of Oestrus ovis myiasis, which is primarily a disease of sheep and goats, with humans becoming accidental hosts, often through direct contact or proximity to infested animals [7]. The presence of myiasis in individuals with a “medium to high socio-economic level” and who are immunocompetent is particularly interesting. While myiasis is often associated with poor hygiene, debility, or immunocompromised states [8,9], our cases suggest that even otherwise healthy individuals in appropriate epidemiological settings are at risk. This underscores that myiasis should not be dismissed solely based on patient demographics or general health status, as highlighted by Ravichandran et al. [2].

4.4. Treatment and Outcomes

The successful treatment protocol involving nasal lavages with saline mixed with an anthelminthic (albendazole), along with systemic corticosteroids and antihistamines, resulted in rapid clinical improvement within an average of 4 days. This aggressive approach, combining mechanical removal or expulsion inducement with antiparasitic agents and anti-inflammatory measures, is consistent with best practices reported in the literature [10]. Manual extraction of larvae via endoscopy is often difficult to practice due to the mobility of the larvae in the nasal cavity, the use of substances that irritate or asphyxiate the larvae (like anthelminthics) can aid in their expulsion. The favorable outcomes in all our cases, without reported recurrences or severe complications, highlight the effectiveness of prompt and appropriate management.

4.5. Limitations

Our study’s main limitation is its retrospective nature and the relatively small sample size of thirteen cases. Although invaluable for a rare disease, this limits the scope for generalization. Furthermore, precise larval staging and complete species identification were not possible in three cases.

5. Conclusions

Our series of fourteen immunocompetent patients with nasal myiasis highlights the crucial importance of including this rare disease in the differential diagnosis of atypical or treatment-resistant rhinitis-like symptoms. The initial presentation may show a striking resemblance to allergic rhinitis, underscoring the need for a thorough clinical examination, including prompt nasal endoscopy. A high index of suspicion, particularly in patients with epidemiologically relevant exposure or symptoms that deviate from typical allergic patterns, is crucial for early diagnosis and effective management, preventing potential complications and ensuring a favorable prognosis.