In the last half century, the life expectancy of beta-thalassemia patients has strikingly increased mostly due to regular blood transfusions and chelation treatments. The improved survival, however, has allowed for the emergence of comorbidities, such as hearing loss, with a non-negligible impact on the patients' quality of life. This thorough review analyzes the acquired knowledge regarding hearing impairment in this hereditary hemoglobinopathy, aiming at defining its prevalence, features, course, and possible disease- or treatment-related pathogenic factors. Following PRISMA criteria, we retrieved 60 studies published between 1979 and 2021. Diagnostic tools and criteria, forms of hearing impairment, correlations with beta-thalassemia phenotypes, age and sex, chelation treatment and laboratory findings including iron overload, were carefully searched, analyzed and summarized. In spite of the relatively high number of studies in the last 40 years, our knowledge is rather limited, and large prospective studies with homogeneous diagnostic tools and criteria are required to define all the aforementioned issues. According to the literature, the overall prevalence rate of hearing impairment is 32.3%; age, sex, and laboratory findings do not seem to correlate with hearing deficits, while the weak relationship with clinical phenotype and chelation treatment seems to highlight the presence of further yet to be identified pathogenic factors.

The aim of this study is to evaluate eye structures and function in patients receiving iron chelating therapy and to assess whether a correlation exists between the onset of ocular alterations and the intake of iron chelating drugs.

A prospective cohort study was performed. Eighty-eight patients, composed of children and adults with thalassemia major (TM) who are taking or had taken iron chelating drugs (deferoxamine, deferiprone or deferasirox), have been initially enrolled in the study. The final sample featured 80 patients, including 18 children and 62 adults. These subjects received an eye examination to evaluate intraocular pressure (IOP), best corrected visual acuity (BCVA), the presence of refractive defects, cornea, anterior chamber, lens, fundus oculi, visual field and mean retinal nerve fiber layer (RNFL) thickness. Logistic regression model analysis was performed in order to assess any correlation. In addition, a literature search regarding the relation between iron chelating drugs and ocular adverse events was carried out to compare the results obtained with the evidence in the literature.

Logistic regression did not report a significant correlation between the intake of iron chelating drugs and the onset of anterior ocular segment alterations, lens opacities, retinal diseases, optical neuropathies, astigmatism, visual field and RNFL thickness defects. Logistic regression returned a statistically significant correlation between myopia and iron chelation therapy (p-value 0.04; OR 1.05) and also between presbyopia and total duration of therapy with deferoxamine (p-value 0.03; OR 1.21). Although intraocular pressure levels remained within the normal range, a significant correlation with the length of deferoxamine therapy has been found (p-value 0.002; association coefficient -0.12). A negative correlation between deferiprone and presbyopia has also been observed.

Iron chelation therapy is not associated with severe visual function alterations. Limitation of deferoxamine treatment can help prevent ocular complications. Deferiprone and/or deferasirox may be preferable, especially in patients over age 40 years.

Life-long transfusion therapy with chelators is a treatment choice for patients with β-thalassemia major. Some investigators have proposed auditory impairment related to the use of deferoxamine, but the mechanisms remain unclear and whether or not deferiprone has similar side effects needs to be evaluated.

Thirty-seven patients with β-thalassemia major who received regular transfusion in our hospital were enrolled. Chelation agents, including deferoxamine and deferiprone, were used. To assess audiologic function, otoscopy, pure tone audiometry (PTA), tympanometry, transient evoked oto-acoustic emission (TEOAE), and auditory brainstem response (ABR) were conducted. Bithermal caloric test was performed to evaluate vestibular function.

All of the 37 patients had normal findings on otoscopic evaluation and their tympanograms were type A. Thirteen patients (35.1%) had hearing impairment at one or more frequencies as detected by PTA. Compared to those without hearing impairment, patients with hearing impairment had lower serum ferritin levels (P = 0.01). Seven of 21 patients (33.3%) failed to pass the TEOAE, while 13 (61.9%) had abnormal ABR findings. Sixteen patients (80%) had canal paresis in the caloric test.

The incidence of auditory impairment and vestibular dysfunction was high in patients with β-thalassemia major receiving long-term transfusion therapy. Potential lesions of auditory impairment may exist anywhere along the auditory pathway, from the inner ear to the brainstem. Lower serum ferritin levels may be associated with hearing impairment. Therefore, regular check-ups of serum ferritin levels and periodic audiologic assessment are mandatory.

Over the years, several reports have demonstrated involvement of the nervous system in beta-thalassemia patients. Neurological complications have been attributed to various factors such as chronic hypoxia, bone marrow expansion, iron overload, and desferrioxamine neurotoxicity. In most cases, neurological involvement does not initially present with relevant signs or symptoms (i.e., is subclinical) and can only be detected during neurophysiological or neuroimaging evaluation. Abnormal findings in the visual, auditory, and somatosensory evoked potential recordings are mainly attributed to DFO neurotoxicity. On the other hand, nerve conduction velocity abnormalities are associated either to chronic hypoxia and older age or to hemosiderosis, whether by means of pancreas involvement or not. Neuropsychological studies available reveal a considerably high prevalence of abnormal IQ, not correlating, however, to factors such as hypoxia or iron overload. It is proposed that factors associated to severe chronic illness, rather than the disease per se, could be responsible for these findings. Such factors include regular school absence due to transfusions and frequent hospitalizations, physical and social restrictions resulting from the disease and its treatment, abnormal mental state due to the awareness of being chronically ill, and, last, the overly protective family attitude that leads to restricted initiative and psychosocial development. As life expectancy for beta-thalassemia patients extends, the use of neurophysiologic and neuropsychologic monitoring becomes imperative, enabling early detection of neural pathway impairment and allowing for appropriate management, in order to achieve a better life quality for this patient group.

As more effective management and even cure of thalassemia become possible, attention is beginning to be directed to the potential neurologic and resulting neurocognitive effects of this illness on adults and children. Recent studies indicate that for adults with beta-thalassemia major and intermedia, and for children with sickle beta-thalassemia (Sbeta-thalassemia), there is a substantial risk for silent brain infarcts that may be associated with neurocognitive impairment similar to that reported for children with sickle cell anemia. Here the available literature in this area is reviewed and the limited outcomes are compared with those available from large, multicenter longitudinal studies of sickle cell anemia. On the basis of these comparisons, it is recommend that children with thalassemia be screened for specific neuropsychological impairments and that they be provided early intervention and special education access as available under the Individuals with Disabilities Education Act (IDEA) or the 504 Regulations of the Rehabilitation Act of 1973.

Gallbladder and gastrointestinal motility defects exist in gallstones patients and to a lesser extent in pigment gallstone patients. To investigated the role of gallbladder and gastrointestinal motility disorders in pigment gallstone formation in beta-thalassemia major.

Twenty-three patients with beta-thalassemia major (16 females; age range 18-37 years) and 70 controls (47 females, age range 18-40 years) were studied for gallbladder and gastric emptying (functional ultrasonography), orocecal transit (OCTT, H(2)-breath test), autonomic dysfunction (sweat-spot, cardiorespiratory reflex tests), bowel habits, gastrointestinal symptoms and quality of life (all with questionnaires). Gallbladder content (ultrasonography) was examined before and during 8-12 mo follow-up.

Gallstones and/or biliary sludge were found in 13 (56%) patients. beta-thalassemia major patients had increased fasting (38.0+/-4.8 mL vs 20.3+/-0.7 mL, P = 0.0001) and residual (7.9+/-1.3 mL vs 5.1+/-0.3 mL, P = 0.002) volume and slightly slower emptying (24.9+/-1.7 min vs 20.1+/-0.7 min, P = 0.04) of the gallbladder, together with longer OCTT (132.2+/-7.8 min vs 99.7+/-2.3 min, P = 0.00003) than controls. No differences in gastric emptying and bowel habits were found. Also, patients had higher dyspepsia (score: 6.7+/-1.2 vs 4.9+/-0.2, P = 0.027), greater appetite (P = 0.000004) and lower health perception (P = 0.00002) than controls. Autonomic dysfunction was diagnosed in 52% of patients (positive tests: 76.2% and 66.7% for parasympathetic and sympathetic involvement, respectively). Patients developing sludge during follow-up (38%, 2 with prior stones) had increased fasting and residual gallbladder volume.

Adult beta-thalassemia major patients have gallbladder dysmotility associated with delayed small intestinal transit and autonomic dysfunction. These abnormalities apparently contribute together with haemolytic hyperbilirubinemia to the pathogenesis of pigment gallstones/sludge in beta-thalassemia major.

Changes in the optic nerve due to the breakdown of blood elements and the effect of deferoxamine on these changes were evaluated.

The study group consisted of 12 rabbits. Three rabbits were used as control. In Group I, three rabbits had bilateral retrobulbar haematoma induced. In Group II, three rabbits had bilateral retrobulbar haematoma induced and were given systemic deferoxamine. In Group III, three rabbits were only given deferoxamine. At day 21, all the rabbits underwent bilateral enucleation and specimens from the orbital fat tissue were removed for light microscopic examination. The optic nerves were examined by light and electron microscopy.

Light microscopic examination of the optic nerves did not reveal significant differences among the groups. Electron microscopy revealed ultrastructural changes in Group I. There were no significant pathological findings observed in Groups II or III. There was abundant iron pigment in the orbital fat tissue of Group I, but only a small amount in Group II.

Systemic deferoxamine treatment is effective in preventing degenerative changes in retrobulbar haema-toma.

Forty patients with beta-thalassemia major (BTM), between 11 and 19 years of age and maintained on long-term desferrioxamine (DFO) treatment, were examined by evoked potential and nerve conduction velocity studies to investigate a possible involvement of the auditory, visual, somatosensory, or peripheral nervous pathways. Pathologic findings in brainstem auditory-, visual-, and somatosensory-evoked potentials, and nerve conduction velocity studies were demonstrated in 25%, 15%, 7.5%, and 25% of the patients, respectively, whereas 15% demonstrated involvement of multiple neural pathways. Subclinical involvement of the auditory pathway was statistically associated with higher mean daily DFO dose and longer duration of DFO therapy, whereas abnormalities regarding the somatosensory pathways were related to older age, longer mean duration of DFO therapy, and lower serum copper levels. Involvement of the peripheral nervous system was related to lower serum copper levels. Multiple involvement of neural pathways was related to longer mean duration of DFO therapy. We conclude that risk factors related to long-term DFO treatment are only partly responsible for the subclinical involvement of neural pathways demonstrated in beta-thalassemia major patients.

Neurophysiologic investigations were performed in 34 Chinese patients with beta-thalassemia major maintained on long-term desferrioxamine treatment to look for subclinical toxicity in the auditory, visual, peripheral, or central neural pathways. In the auditory pathway study, four patients (12%) had mild sensorineural hearing impairment. Two patients (6%) had increased P 100 latencies in the visual evoked potential study, and nine patients (26%) had abnormal electroretinogram results. All had normal electrooculograms. Ophthalmoscopic examination was abnormal in three patients (9%), and three (9%) had a visual field defect. In the peripheral or central nervous pathways, seven patients (21%) had sensory neuropathy, of which three cases were probably related to diabetes mellitus. All had normal motor conduction velocities. Four patients (12%) had increased cortical latencies of median or posterior tibial somatosensory evoked potential. Abnormalities in multiple neural pathways were seen in four patients (12%). There was a significant association between subclinical toxicity to the peripheral or central nervous systems and serum ferritin level (P < .03) and the presence of diabetes mellitus (P < .002). There was no significant relationship between the age, dosage, or duration of desferrioxamine used and the increased risk of neurotoxicity to the auditory, visual, peripheral, or central nervous systems. There was also no association between the risk of neurotoxicity and the serum zinc, copper, or fructosamine levels.

Clinical observations were made of 42 children with bilateral idiopathic progressive sensorineural hearing loss considering hearing loss distribution in relation to age at onset, audiometric features, audiologic characteristics and possible correlation with some haematochemical alterations. Patients were divided into 2 groups on the basis of hearing onset: Group I, 0-6 years; Group II, 7-14 years. A peak in the distribution of onset age was observed in the range of 4-6 years. In most cases a 'descending' curve was recognized accompanied by recruitment. The haematochemical tests only suggested a possible correlation between hearing loss and anaemia. Finally, no significant difference of incidence between the sexes was observed.

Tissue damage involving oxygen-derived free radicals may be greatly exacerbated by free, reactive iron, which acts as a catalyst in oxidative reactions. The effects of free iron can be attenuated by the administration of deferoxamine (DFO), an iron chelator. However, DFO has limited therapeutic utility because it has a short plasma half-life (approximately 5.5 min in mice) and produces profound hypotension upon intravenous infusion. These negative attributes have been circumvented by the covalent attachment of DFO to large polymers, such as dextran or hydroxyethyl starch. The ability of the dextran-conjugated DFO (DEX-DFO) to inhibit iron-catalyzed reactions with lipids was compared to that of the native molecule in an in vitro model of CNS lipid degradation in the presence of 200 microM ferrous iron. There was no difference between native DFO and the modified form. Modified and unmodified DFO were also compared for therapeutic efficacy in a murine model of head injury. Using a previously described "grip test" as a measure of neurologic impairment following injury, DEX-DFO, native DFO, and dextran were administered intravenously 3-5 min after injury. Dextran-DFO significantly decreased the incidence of severe neurologic impairment at dosage levels of 0.1 (n = 92), 1.0 (n = 76), and 10.0 (n = 80) mg/kg. Administration of native DFO or dextran had no effect at the same dosages and concentrations. These results suggest that the murine model of head injury contains a significant iron-dependent component that should be assessed in other models of neural injury.