In our case series, we reported two cases that presented with surgical or trauma-related perichondritis. Both had undergone multiple debridement treatments and negative pathogenic bacterial and fungal culture results throughout their disease course. To make matters worse, they experienced a failure to respond to intravenous broader spectrum antibiotic treatments that should be appropriate for common bacteria. Thankfully, these two patients were eventually confirmed to have fungal infections by mNGS and received antifungal therapy. Their infection was then controlled within two weeks, and the patients developed no obvious deformities. Therefore, we believed that fungi may also be the pathogenic bacteria of suppurative perichontitis. Our results suggested that mNGS is a powerful tool in the diagnosis of perichondritis of the auricle and has a wide range of application prospects in the differential diagnosis of ear infections.

Suppurative perichondritis always involves the perichondrium and the chondral cartilage and causes abscess formation and cavitation of these structures. Improper treatment can lead to cosmetic sequelae, especially after ear surgery, making the treatment by otolaryngologists less cosmetic [5]. At present, Pseudomonas aeruginosa is considered the main pathogenic bacteria, which may be related its special affinity to damaged auricular cartilage. Other suspected pathogens that have been reported include Staphylococcus aureus and Escherichia coli [5]. The treatment of perichondritis mainly relies on appropriate antibiotics, which are based on the culture results, for Pseudomonas aeruginosa, and the antibiotics are used in combination with debridement. The vast majority of cases recover with no sequelae. However, the infection can become uncontrollable in some cases, resulting in permanent deformities. In these cases, the patient undergoes multiple surgeries and is given multiple antibiotics throughout the disease course, but the patient still ends up with a “cauliflower ear” [6]. Some studies have revealed that antibiotic resistance and autoimmune response mechanisms may cause these uncontrolled infections [4]. However, the cause of these uncontrolled infections is frustratingly unknown.

Recently, mNGS has become an emerging method for diagnosing nonculturable microorganisms and is relatively effective in classifying and identifying pathogens, especially when the results of conventional culture are negative. mNGS is a pathogen metagenomics technology that does not rely on traditional microbial culture but rather directly extracts all nucleic acids from specimens for high-throughput sequencing. Through the analysis of biological information, the human sequence was removed, and the screened data were compared with the pathogen database to obtain the species information of suspected pathogenic microorganisms [7]. mNGS is unbiased, has wide coverage, has high sensitivity and is fast. Compared with traditional culture-based pathogen detection techniques, mNGS has the characteristics of fast detection speed, variety and high sensitivity, and has gradually become an important role in the detection of difficult and unknown pathogenic microorganisms in clinic means. However, the high cost of mNGS is not conducive to widespread promotion, and it should be used as a supplementary test for negative traditional detection methods. As a new technology for pathogen detection, mNGS has been preliminarily applied in the detection of invasive fungal sinusitis and necrotizing otitis externa in recent years, improving patient prognosis [8, 9, 10]. In our case series, both of them had multiple negative pathogenic bacterial and fungal culture results throughout their disease course. Then mNGS was used to identify the fungal infections, and good outcomes were achieved.

Collectively, we first presented a series of uncommon cases of perichondritis of the auricle. When infection occurs in patients with negative culture results, a fungal infection should be considered, and the patient and managing team should be warned of the possibility of a fungal infection. mNGS is a promising additional technique for identifying specific infections.