Teaching Case

A 60-year-old female presented with bilateral long-term hearing loss, with no other symptoms. Otologic examination showed no alterations, but audiometry demonstrated bilateral mixed-type hearing loss (Figure 1).

Blood analysis revealed elevation in alkaline phosphatase (157 U/L).

A CT scan was requested to evaluate the cause.

Temporal one CT showed extensive, diffuse demineralisation of bony structures at the base of the skull, especially in the petrous apex (Figure 2), and diffuse sclerosis of the otic capsule bilaterally (Figure 3). The internal auditory canals were found normal (Figure 4), and the ossicular chain was preserved bilaterally (Figure 5). A dehiscence of the right superior semicircular canal was also observed (Figures 6a and 6b).

Subsequently, the patient performed whole-body technetium 99 scintigraphy that demonstrated an intense radionuclide uptake on the cranial vault and facial bones, excluding the mandible (Figure 7).

The findings on CT (especially the diffuse sclerosis of the otic capsule bilaterally and the preservation of the ossicular chain) and on scintigraphy were consistent with polyostotic Paget's disease of bone (PDB).

PDB is a chronic disorder characterised by anomalies in bone remodelling resulting in abnormal bone formation, affecting one (monostotic) or more (polyostotic) bones. It most commonly involves the spine, skull, pelvis, and long bones of the lower extremity [1,2]. It is characterised by an increased number and activity of osteoclasts followed by increased, although disorganised, bone formation by osteoblasts, leading to woven bone formation [3].

Most patients are asymptomatic. The involvement of the skull may lead to hearing loss (such as in the present case), headache and cranial neuropathies [1].

The mechanism of hearing loss in PDB is not well understood, but it is believed to be cochlear. Monsell et al. [4] demonstrated a correlation between bone mineral density of the cochlear capsule and both the high-frequency pure-tone air conduction thresholds and the low-frequency air-bone gap, suggesting that the latter is not caused by ossicular chain disease, but rather by derangement of the acoustic mechanics of hearing. These authors also show that the auditory nerve function is preserved in PDB, which helps support the cochlear dysfunction hypothesis. Another proposed mechanism refers to abnormalities of cochlear metabolic homeostasis, namely secondary to cytokine release from the pagetic bone [5], but this is yet to be confirmed.

The diagnosis is based on a combination of symptoms, physical examination, laboratory findings and imaging tests. The increased rate of bone turnover leads to an elevated level of serum alkaline phosphatase. The disease has characteristic features on X-ray, including osteolytic areas, cortical and trabecular thickening and osteosclerosis [1]. Bone scintigraphy is the most sensitive test [2], and like in this case, sites of involvement have intense and homogeneous radionuclide uptake. Other imaging techniques, such as CT or MRI, may be helpful in evaluating the extent of the disease and the presence of complications such as basilar invagination and osteosarcoma [3]. In this case, considering that hearing loss was the only symptom and that the CT and scintigraphy confirmed the diagnosis, radiographs and MRI were not requested.

Additionally, this patient’s CT demonstrated a right superior semicircular canal dehiscence, which we considered an incidental finding, since the patient did not have any other symptoms that may suggest a third window syndrome. Furthermore, the Hennebert and Tullio signs were absent.

Treatment may include anti-resorptive agents, analgesic and anti-inflammatory drugs. This patient was treated with bisphosphonates and a bilateral hearing aid, given the irreversibility of the hearing loss.

All patient data have been completely anonymized throughout the entire manuscript and related files.