Loss of sight and sound. Could it be the hip?

In September, 2007, a 58-year-old woman was admitted to our neurology department because of progressive visual and hearing loss which had started 9 months earlier. She had type 2 diabetes and hypertension, both of which were adequately controlled by medication. In 2001, she had a left hip arthroplasty which was revised in October, 2006 because of rupture of the ceramic head. 3 weeks before admission, investigations showed a mild hypothyroidism of unknown origin, which was treated with levothyroxine sodium. The neurological examination at admission showed impairment of cranial nerves II and VIII bilaterally and mild distal sensory-motor dis turbances. Laboratory investigations ruled out haema tological, infectious, neoplastic, metabolic, and immuno logical diseases. Concomitantly our patient underwent various investigations including brain MRI (showing hyperintensity of optic nerves and tracts), electromyography (showing mild lower limb nerve amplitude reduction), and acoustic and visual evoked potentials (positive for bilateral absence of brainstem acoustic responses and irregular cortical visual responses). A working diagnosis of axonal multi-neuropathy caused by a presumed immune-mediated vasculitis was made and the patient was given prednisone (50 mg/day) for 2 months with little improvement. By December, 2007, our patient became completely blind, severely deaf, and wheel-chair bound because of lower limb hyposthenia. Tests for immune-mediated process remained negative and the case was referred to toxicology for further investigation. Unexpectedly, raised concentrations of cobalt and chromium were found in diff erent biological samples (cobalt: 24 h urine collection 1187 μg/L [0·1–1·5], blood 549 μg/L [0·05–2·7], plasma 90 μg/L [0·1–0·6], CSF 11·4 μg [0·05–0·15]; chromium: 24 h urine collection 510 μg/L [0·05–2·2], blood 54 μg/L [0·1–0·5], plasma 210 μg/L [0·1–0·5], CSF 4·4 μg/L [0·01–0·2]). Cobalt-chromium poisoning due to metal wear debris from her hip prosthesis was proposed, although radiology, including CT, showed no sign of prosthesis loosening. In February, 2008, several metal ion chelating treatments were given with edetic acid. Although metal ion concentrations decreased, neurological improve ment was negligible. Therefore, in April, 2008, resection arthroplasty was done. During surgery infi ltration of the peri-prosthesic tissue by metallic debris was evident (fi gure A); analysis of peri-prosthetic fl uids showed high concentrations of cobalt and chromium, and the removed prosthesis showed wear of the head and neck (fi gure B), supporting the hypothesis of endogenous cobalt-chromium poisoning. During the following 8 months the patient showed progressive improvement, although vision only partially improved. Metal ion concentrations decreased but remained higher than reference values at the last follow-up in November, 2008. The role of cobalt or cobalt-chromium on human tissues has not been defi nitively established. Cobalt can produce various toxicological eff ects including local respiratory symptoms due to inhalation of cobalt containing dusts, and systemic eff ects (thyroiditis, cardiomyopathy, erythropoiesis). Neuro logical toxicity, mainly optic atrophy, nerve deafness, and limb paraesthesia, has been occasionally reported in association with exogenous exposure. Neuro logical toxicity as a reult of endogenous exposure (mainly associated with metal prostheses) has been described. Cobalt can induce a hypoxia-like eff ect, possibly targeting mitochondria; of note, our patient’s symptoms were similar to those observed in some mitochondrial cytopathies. Total hip replacement and hip resurfacing arthroplasty are widely used therapeutic procedures; longer-term follow-up would be necessary to evaluate adverse chronic systemic eff ects due to prolonged exposure to high serum cobalt concentrations. In addition to orthopaedic evaluation, careful neurological and toxicological examinations are recommended whenever a patient with a metallic prosthesis complains of visual loss, hearing disturbance, limb weakness, numbness, or paraesthesia, even in the absence of local osteoarticular symptoms.