Introduction
The pregnant woman goes through a series of physiological changes throughout her pregnancy which affect her in a variety of ways. The changing levels of sex hormones exert an influence on the functioning of the sensory nervous system, which can result in hearing problems.Reference Sennaroglu and Belgin1
Sudden deafness is a distressing albeit rare occurrence in pregnancy. It is defined as a rapid decline in hearing (i.e. more than 30 dB sensorineural hearing loss over less than three days) in at least three contiguous frequencies, without any accountable cause.Reference Wang and Young2
The management of sudden deafness occurring in pregnant patients has proved challenging due to limited clinical experience. This is compounded by obstetric complexities such as potential fetal adverse effects of treatment.
This paper aims to address the quandary of sudden deafness in pregnancy and its management by reviewing the existing literature on the subject. Specific focus has been given to the aetiology, investigation findings and treatment of this clinical problem.
Methods
Relevant articles were identified from electronic databases (PubMed (MEDLINE), Ovid (MEDLINE), all EBM Reviews (Cochrane DSR, ACP Journal Club, DARE and CCTR) and EMBASE) using key word searches for ‘sudden hearing loss and pregnancy’ and ‘sudden deafness and pregnancy’. Due to the scarcity of literature pertinent to this subject, all studies identified were included in this review. A hand search of the reference lists of retrieved papers was also conducted. Studies that examined hearing loss in non-pregnant women with varied hormone profiles were also assessed in order to better understand the effects of female hormonal changes on hearing loss.
Aetiology
The hormonal system in the pregnant woman undergoes unique changes to maintain an optimal condition for pregnancy. Such changes include considerably increased oestrogen and progesterone production rates compared with the non-pregnant state.Reference Sennaroglu and Belgin1 This marked increase in hormone levels is the basis of many theories explaining the possible relationship between hearing loss and pregnancy.
One hypothesis is that increased sex hormones pose a thrombogenic risk and can interrupt cochlear microcirculation, leading to the development of sudden deafness.Reference Lavy3 Similarly, pregnancy causes a hypercoagulable state in which there is decreased erythrocyte deformability, increased plasma viscosity and erythrocyte aggregation.Reference Wang and Young2 All these factors lead to an increased risk of thromboembolic episodes of the cochlear artery.Reference Lavy3 Such hormonal alterations also lead to an increase of approximately 6.5 l of extracellular fluids and 1.2 l of intracellular fluid, resulting in osmotic disturbances due to water and sodium retention.Reference Sennaroglu and Belgin1, Reference Pawlak-Osinska, Burduk and Kopczynski4 Sennaroglu and BelginReference Sennaroglu and Belgin1 have proposed that this shift in fluid osmolarity could affect the inner ear and cause a low frequency hearing loss pattern resembling Ménière's disease.
The above assumptions are based on the systemic effect of sex hormones. Much effort has been made to investigate the direct effects of oestrogen on the auditory pathway. There are two intracellular oestrogen receptors, labelled α and β.Reference Hultcrantz, Simonoska and Stenberg5 Stenberg et al. Reference Stenberg, Wang, Fish, Schrott-Fischer, Sahlin and Hultcrantz6 have shown that oestrogen receptor α is present in the spiral ganglion and oestrogen receptor β in the stria vascularis, locations vital for hearing transmission and inner ear homeostasis. However, it is still unclear whether these structures have true target cells, as the direct effect of oestrogen on such cells has not been proven to date.Reference Hultcrantz, Simonoska and Stenberg5
Case reports of the hearing levels of women with different hormonal levels have given conflicting findings, making it difficult to draw a conclusion.Reference Hultcrantz, Simonoska and Stenberg5 Cyclic hearing alterations during different stages of the menstrual cycle have been reported by Yadav et al.,Reference Yadav, Tandon and Vaney7 Cox,Reference Cox8 and Swanson and Dengerink.Reference Swanson and Dengerink9 Kilicdag et al. Reference Kilicdag, Yavuz, Bagis, Tarim, Erkan and Kazanci10 have shown that oestrogen therapy, in the form of hormone replacement therapy (HRT), appears to slow down hearing loss in postmenopausal women. This proposal has been supported by Kim et al.,Reference Kim, Kan, Chae and Kim11 who have reported that lower levels of oestradiol seem to impede hearing sensitivity in postmenopausal women. However, there have been isolated case reports of acute deafness caused by the use of the oral contraceptive pillReference Hanna12 and HRT,Reference Strachan13 both situations in which oestrogen levels are increased.
Despite the above reports, the oestrogen surge during pregnancy is unique, making it difficult to determine from previous case descriptions whether acute deafness in pregnancy is due to the direct effects of oestrogen on the auditory pathway.
Audiological investigations
There are few published reports correlating audiological investigation findings with sudden hearing loss in pregnancy.
Sennaroglu and BelginReference Sennaroglu and Belgin1 investigated the effect of pregnancy on hearing levels by studying 20 pregnant women with no hearing complaints. A gradual decrease in pure tone averages (at 125, 250 and 500 Hz) from the first trimester (i.e. up to 14 weeks) to the third trimester (i.e. 29–42 weeks) was found. However, this hearing loss did not reach pathological levels, and hearing returned to normal in the postpartum period. Hearing at frequencies higher than 500 Hz showed no significant change.
On the other hand, Tsunoda et al. Reference Tsunoda, Takahashi, Takanosawa and Shimoji14 found that pure tone audiometry and impedance audiometry showed normal hearing in all their 56 pregnant women complaining of ear problems.
The only study assessing brainstem auditory evoked potential responses in pregnancy was performed by Tandon et al. Reference Tandon, Misra and Tandon15 These authors demonstrated an increase in the evoked wave V threshold in eight pregnant women. The wave I–V interpeak latencies were also significantly greater than in the control group. However, the authors did not comment on whether these changes in brainstem auditory evoked potential could contribute to sudden hearing loss in pregnancy.
Treatment options
There is no current consensus on the treatment of sudden hearing loss in pregnancy, as patient groups are small.
The only successful treatment agent reported thus far is dextran 40, a form of colloid solution used as a plasma expander. Wang and YoungReference Wang and Young2 have shown that this treatment significantly improved the incidence of hearing improvement in a group of pregnant patients with acute deafness. Dextran 40 decreases blood viscosity and enhances microcirculation, and hence reduces cochlear hypoxia.Reference Wang and Young2 Although Wang and Young's study found a significant difference in hearing improvement between the dextran and control groups (83 versus 20 per cent, respectively), patient numbers were small (with six patients in the dextran group and five in the control group) due to the rarity of this clinical problem. Unfortunately, dextran does not come without adverse effects; those reported include renal failure, coagulopathy and non-cardiogenic pulmonary oedema.Reference Kuo, Hsu and Young16 Thus, the potential benefits and risks need to be weighed before commencing treatment.
Another proposed treatment for idiopathic sudden hearing loss is steroid therapy,Reference Wilson, Byl and Laird17 which works via either a reduction in inflammation or a direct effect on the inner ear neuroepithelium.Reference Wang and Young2 Despite promising research findings, this treatment method has never been tested on pregnant women. It is in fact not recommended in this patient group, as excessive prenatal exposure can cause detrimental fetal effects such as alteration of the metabolic and endocrine balance of various organs.Reference Wang and Young2
The natural history of sudden sensorineural hearing loss in pregnant women has not been established, although spontaneous resolution is common in adult men and non-pregnant women in up to 75 per cent of cases.Reference Cinamon, Bendet and Kronenberg18 Recovery may be complete or partial.
Acoustic neuroma
Wang and YoungReference Wang and Young2 have reported a case of acoustic neuroma which presented as ipsilateral sudden deafness, facial palsy and vertigo in a pregnant woman of 31 weeks' gestation.
Acoustic neuroma is a benign intracranial tumour of the vestibular nerve myelin sheath. Even though it presents infrequently in pregnant women, this tumour has been shown to expand rapidly during pregnancy, possibly due to hormonal changes.Reference Beni-Adani, Pomeranz, Flores, Shoshan, Ginosar and Ben-Shachar19, Reference Doyle and Luxford20 The increase in size and vascularity of the lesion can lead to acute bleeding, which causes exacerbation of symptoms.Reference Kachhara, Devi, Nair, Bhattacharya and Radhakrishnan21 Non-specific symptoms of headache, nausea and tinnitus, commonly attributed to pregnancy itself, may delay the diagnosis of acoustic neuroma in pregnant women.Reference Beni-Adani, Pomeranz, Flores, Shoshan, Ginosar and Ben-Shachar19, Reference Gaughan and Harner22
Once the diagnosis is made via magnetic resonance imaging, as in Wang and Young's case,Reference Wang and Young2 a multidisciplinary approach is required involving obstetricians, neurosurgeons and anaesthetists. Management is dependent on the gestational stage of the pregnancy and the neurological status, with severe symptoms necessitating urgent surgical intervention.
Surgery performed during the first trimester poses the greatest anaesthetic risk to the fetus, in terms of spontaneous abortion and fetal teratogenicity.Reference Wang and Young2, Reference Beni-Adani, Pomeranz, Flores, Shoshan, Ginosar and Ben-Shachar19, Reference Doyle and Luxford20
The anaesthetic risk to the mother increases during the later stages of pregnancy, due to physiological changes such as reduction in functional residual respiratory capacity and expansion of blood volume causing alteration of anaesthetic drug distribution.Reference Doyle and Luxford20 Provided there are no impending neurological complications, surgical intervention can be safely delayed until the postpartum period.Reference Gaughan and Harner22 If the lesion is large and symptoms are severe due to obstructive hydrocephalus, early ventriculoperitoneal shunting alone could be performed, followed by tumour resection after delivery.Reference Sharma, Pundir and Sharma23
If the patient is in an advanced stage of pregnancy, the best fetal and maternal outcomes are provided by emergency Caesarean section after drainage of cerebrospinal fluid, followed by definitive neurosurgery.Reference Beni-Adani, Pomeranz, Flores, Shoshan, Ginosar and Ben-Shachar19
Conclusion
Sudden hearing loss is a rare occurrence during pregnancy, leading to a dearth of literature due to limited clinical experience. The audiological investigation findings of such patients remain equivocal. Spontaneous recovery may occur during the postpartum period. In patients who require medical treatment, dextran 40 infusion can be employed, after careful weighing of potential benefits versus adverse effects. The diagnosis of acoustic neuroma needs to be considered in patients presenting with associated symptoms which manifest at the time of presentation of sudden deafness. There remains scope for further research, in the form of larger studies, to ascertain the best management option for this clinical problem.
