Type 2 diabetes mellitus (T2DM) is an important global health issue. According to the International Diabetes Federation (IDF), 537 million adults were living with diabetes in 2021. The predictions for future years are worrying. According to the same organization, the number of patients diagnosed with this condition will reach 643 million by 2030 and 783 million by 2045(1). Several studies have shown that diabetic patients have an increased risk of infection. The possible factors involved are represented by altered cellular and humoral immune defense mechanisms, poor vascular flow to sites of infection, and microvascular complications(2). The disease can generate numerous complications, including otorhinolaryngologic disorders. This article presents an overview of the available information based on articles published on PubMed and Google Academic.
Otorhinolaryngologic infections disease
Type 2 diabetes mellitus is a risk factor for deep neck infection. Peritonsillar abscesses is a common disease, being defined by the localized polymicrobial infections between the fibrous capsule of the tonsil and the superior pharyngeal constrictor muscle(3). In the etiopathogenesis of the disease, a polymicrobial mixture of aerobes and anaerobes is involved. Some theories suggest that Weber glands, infection, periodontal disease and smoking contribute to the formation of peritonsillar abscesses(4-6).
Wu et al. investigated the risk, prognosis and complications of peritonsillar abscesses in 67,852 patients with T2DM. The results were compared with those obtained from a control group made up of 135,704 subjects without type 2 diabetes mellitus. The results of the study showed that, in patients with T2DM, the incidence of peritonsillar abscesses was relatively high, being 1.73 times higher compared to the one of subjects without type 2 diabetes mellitus. The patients with T2DM should be particularly careful about this condition within one to five years after the diagnosis(7).
In 2017, Pascual et al. published in the Brazilian Journal of Otorhinolaryngology the results of a retrospective study of 330 patients with deep neck infections and peritonsillar infections. In this study, the authors found that systemic comorbidities like diabetes mellitus are bad prognostic factors(8). Similar conclusions were presented in 2014 by Jin and Zhang in a retrospective study of 142 patients with deep neck infection. The authors specify that “the most common underlying systemic disease was diabetes mellitus”(9).
The influence of diabetes on deep neck infection was also evaluated by Lin et al. in a retrospective study of 131 patients. The results of the study showed that deep neck infections were significantly more prevalent in diabetic patients over 60 years old than in nondiabetic subjects of similar age. The diabetic group had a higher complication rate, longer hospital stays and a higher tracheotomy rate compared to the control group(10). In most situations, diabetic patients’ bacteriological investigations highlighted a higher prevalence of culture identification for Klebsiella pneumoniae and a lower prevalence of anaerobes and Streptococcus pneumoniae(11).
Malignant external otitis is an invasive infection that can affect the external auditory canal and the skull base(12-14). The condition affects patients with impaired immune systems and diabetes. The most common symptoms and clinical signs include deep otalgia, chronic otorrhea and cranial nerve involvement(15). Lee et al. performed a retrospective study on prognostic factors in malignant external otitis. Twenty-eight patients diagnosed and treated with this condition were evaluated. Twelve patients who experienced complete remission from malignant external otitis were included in the control group, and the other 16 patients either survived with the disease or died from this condition. Twenty-three patients (82.1%) had diabetes. The results of the study showed that the duration of diabetes and the presence of inflammatory markers influenced the prognosis of malignant external otitis(15).
Franco-Vidal et al. performed a retrospective study, reviewing a series of 46 patients with necrotizing external otitis. Of these, 30 patients had diabetes(16).
Joshua et al. aimed at identifying the risk factors for malignant external otitis in 75 patients hospitalized between 1990 and 2003. The results of the study showed that malignant external otitis “affected mostly diabetic patients and were characterized by granulations and discharge in the external ear, severe prolonged pain, soft tissue involvement and bone destruction on computed tomographic scan, and growth of Pseudomonas aeruginosa in culture”(17).
In 2022, Peled et al. published in the European Archives of Oto-Rhino-Laryngology the results of a study on diabetes and glycemic control in necrotizing otitis externa. Eighty-nine patients were included in the study, of which 83 patients had diabetes. Pre-admission average value of glycated hemoglobin (HbA1c) was 8.13%, and 49 patients had mean glucose above 140 mg/dL. The duration of diabetes was 157.88 months among patients who required surgery and 127.6 months among patients who were treated conservatively. The authors concluded that the value of “HbA1c at admission is associated with longer hospitalization duration” among necrotizing external otitis patients(18).
Auditory acuity in diabetic patients
The incidence of acquired sensorineural hearing loss has increased and may result in permanent hearing disability(19). The affliction occurs due to damage to the inner ear, the auditory nerve or the brain. Other proposed mechanisms are inflammation, oxidative stress and blood flow blood alteration in the inner ear(19,20).
Several studies have reported that diabetic patients have a higher incidence of sensorineural hearing loss than general subjects. This risk has been assessed by Lin et al. in a study that included 26,556 patients with diabetes mellitus and 26,556 nondiabetic patients. The results of the study showed that the incidence of sensorineural hearing loss was 1.54 times higher in the diabetic group compared to the control group. An increased risk of developing sensorineural hearing loss was observed in diabetic patients with comorbidities, as well as retinopathy and renal insufficiency(21).
Krishnappa and Naseeruddin performed a cross-sectional study on 106 patients with T2DM and 90 subjects without diabetes mellitus. The patients and subjects were evaluated by tone audiometry and blood investigations (HbA1c, fasting and postprandial glucose, serum creatinine levels). The results of the study showed that the prevalence of hearing loss was 73% in diabetic patients. The authors concluded that “diabetes mellitus was associated with higher hearing loss compared to presbycusis and hearing threshold was seen to affect all frequencies, but significantly the higher frequencies in diabetics. As the duration of diabetes increased, the severity also increased. Poorer the HbA1c, more severe was the hearing loss”(22).
The incidence of sensorineural hearing loss in patients with type 2 diabetes mellitus was evaluated by Rajendan et al. The study included 60 patients with ages between 40 and 50 years old, with T2DM, and 60 subjects without diabetes mellitus, with matching ages and sexes. The patients and subjects were evaluated by tone audiometry and blood investigations (HbA1c, fasting and postprandial glucose, serum creatinine levels). The results of the study showed a very stark difference in the prevalence of hearing loss: 73.3% in diabetic patients compared to only 6.7% in the control group. The authors mention that the glycemic status and duration of diabetes have no significant correlation with this condition(23).
Hearing loss in T2DM has also been evaluated by Pemmaiah and Srinivas in a cross-sectional study involving 110 patients. Forty-eight patients (43.6%) had bilateral sensorineural hearing loss. Of these, seven patients exhibited severe hearing loss, 16 exhibited moderately severe hearing loss and 25 exhibited moderate hearing loss. The duration of the patients’ diabetes and sensorineural hearing loss revealed a statistically significant correlation(24).
The relationship between diabetes and hearing loss is not completely elucidated. The involved risk factors may be represented by age, duration of the affliction, glycemic control, microangiopathy, neuropathy, and medications used to treat comorbidities. Ototoxic effects can represent side effects of medications such as antibiotics, psychotropics, anticancer agents, antihypertensive and antiarrhythmics, nonsteroidal anti-inflammatory drugs and loop diuretics(25,26). In a review published in 2005 by Maia and Campos, about the hearing loss in diabetic patients, the authors mention that “there are many different types of hearing loss found in diabetic patients. One of them is progressive, gradual bilateral sensorineural loss, affecting especially high frequencies and the elderly. It would be similar to presbycusis, but with more severe losses than those expected by aging. Conversely, there are authors that report the possibility of having early sensorineural loss and others that reported hearing loss in low and medium frequencies. Some studies described diabetes as the possible cause of unilateral sudden loss, but other authors did not find the same association”(25).
This led some researchers to investigate the effects of antidiabetic therapy on hearing loss. Metformin is the most used oral hypoglycemic agent in the treatment of type 2 diabetes mellitus and remains the first choice when treating the affection. A 14-year follow-up study conducted by Chen et al. demonstrated an association between the treatment with metformin and the lower incidence of hearing loss among patients with T2DM(27). Similar results were reported by Miwa et al.(28)
While the link between type 2 diabetes mellitus, deep neck infection and auditory disorders was highlighted in numerous publications, its exact nature and the influencing factors have not yet been elucidated, remaining a keen interest for diabetologists and otolaryngologists alike.
Conflict of interest: none declared
Financial support: none declared
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