Hearing Loss Common in Young Patients With MPS Disorders, Study Finds

Hearing loss is the most common auditory complaint among young patients with different forms of mucopolysaccharidosis (MPS), including Sanfilippo syndrome, a small study suggests.

According to investigators, these findings highlight the importance of routine tests to monitor hearing quality in these patients, and assess when hearing rehabilitation should be started.

The study, “Hearing Loss in Mucopolysaccharidosis,” was published in the journal International Archives of Otorhinolaryngology.

MPS disorders are characterized by deficiencies in lysosomal enzymes that are needed to break down large sugar molecules called glycosaminoglycans (GAGs). There are seven different types of MPS, depending on which lysosomal enzyme is at fault. (Lysosomes are small cell compartments where different types of molecules are recycled.)

MPS are progressive conditions that involve several organs, such as the liver, spleen, heart, blood vessels, bone marrow, bones, lymph nodes, eyes, and ears. Although hearing loss seems to be one of the most common manifestations of these disorders, few studies have investigated the evolution and underlying causes of auditory impairments in these patients.

Now, researchers in Brazil reported the findings of a case series study that aimed to characterize and document the evolution of auditory impairments in MPS patients.

They reviewed the medical records of 24 patients, ages 1 to 21 years (mean 7.3), who had been diagnosed with MPS type I, II, IIIA, IV or VI. Of these, 15 (62.5%) were female, and 20 (83%) had been receiving enzyme replacement therapy (ERT) for an average period of 19.9 months.

ERT is a form of treatment available to treat some forms of MPS. It works by providing patients with a recombinant (man-made) version of the enzyme they are missing.

To assess patients’ hearing quality, researchers reviewed clinical data from previous ear-nose-throat (ENT) evaluations and audiological examinations they had undergone. If none was found, participants had an initial ENT exam performed by an expert physician.

All patients were followed from December 2012 to October 2014. During this time, they had a second ENT evaluation, which was carried out at least six months after their initial examination.

Of the 24 patients included in the study, 15 were able to complete a follow-up audiological assessment. All had been receiving ERT for 1.7 to 14.5 years (average of five years).

At their first ENT evaluation, 37.5% of the patients reported hearing impairment (hypoacusis) and had a history of otitis (inflammation of the ear). Of those, 30% noted a progressive worsening of hearing loss.

A third of the patients (33.3%) presented normal ear examination and only one (4%) had a ruptured eardrum. Tympanic membrane retraction was seen in seven patients (29.1%) in both ears, and in two patients (8.3%) in one ear. (Tympanic membrane retraction is a condition in which a part of the eardrum lies deeper than normal within the ear.)

Among those with tympanic membrane retraction, two had non-infected fluid in the middle ear, behind the eardrum, a condition known as otitis media with effusion.

In initial audiometric evaluations, 18 patients (ages 5–16) who had been on ERT for an average of 2.3 years responded to pure tone and/or vocal audiometry tests. (Both are behavioral tests used to measure  hearing sensitivity.)

Hearing loss was detected in 17 (94.4%) of these patients. Among these, six (35.2%) also complained of hearing impairments. There was a high prevalence of mild hearing loss (75%), followed by moderate hearing loss (18.8%), and only one patient experienced severe hearing loss.

Conductive hearing loss was present in nine patients (56.2%) in both ears, and in one patient (6.2%) in one ear. Two patients (12%) had mixed hearing loss, and two patients had sensorineural loss in both ears. Two patients presented conductive hearing loss in one ear associated with mixed hearing loss and sensorineural loss, respectively.

Hearing loss is said to be conductive, when sound waves are blocked from passing through the ear canal, and sensorineural when caused by problems in the ear’s sensory organ (cochlea, or related structures). It also can be mixed  when it is a combination of both.

At follow-up, 45.4% of the patients complained of hearing loss. Of these, 80% reported a stable progression of hearing impairment, and 20% had otitis in the previous year.

Of the 15 patients who completed follow-up, only two had a normal ear examination in both ears. Tympanic retraction in both ears rose to 60%, and there were more patients with ear alterations.

At follow-up, 14 patients presented audiometric tonal responses (ages 5–20), and from these, 13 (92.9%) showed signs of hearing loss.

While one patient showed signs of hearing improvement between both evaluations, in most cases (85%) those who had mild conductive hearing loss worsened over time.

Overall, these data show that among MPS patients “the most common hearing complaint was hearing loss, which was confirmed by audiology tests in almost 100% of the patients, most of whom presented conductive hearing loss,” the researchers wrote.

“It is important to evaluate the complaints, physical examination, and audiology tests in patients with MPS. The otorhinolaryngologist should be part of the group of professionals that follows these patients to better monitor their hearing and provide early hearing rehabilitation,” they concluded.