The Danish study followed 1,135 women with breast implants and 7,071 women in the comparison breast reduction group. The same neurologic diseases were examined, with the addition of myasthenia gravis, other demyelinating central nervous system neuropathies, and motor neuropathy. Cases were not verified. No increased relative risk for defined neurologic disease in the implant group relative to the comparison group was found. The relative risk in the implant group was 1.7 (95% CI, 0.9-2.9), but a similar excess of neurologic disease was found in the breast reduction control group. The relative risks for several individual neurologic conditions were not significantly elevated, and on chart review, 38% of the cases (5 of 13) of neurologic disease were discovered to have had their onset before breast implantation (Winther et al., 1998).
Another recent publication addressed the issue of sensorineural hearing loss (Meniere's disease) associated with silicone breast implants. A group of 119 of 184 women with Meniere's disease or progressive hearing loss and 100 age-matched controls responded to questionnaires (64.7% response rate) and provided serum samples to measure the presence of the 68 kiloDalton (kDa) protein found in some forms of autoimmune hearing loss. There was no significant association of silicone breast implants with Meniere's disease or progressive hearing loss (odds ratio, 1.42). The presence of the 68-kDa protein was not significantly associated with the presence of silicone breast implants (Kim and Harris, 1998). The committee has concluded that these well-designed epidemiological studies provide limited evidence for the lack of association between breast implants and neurologic disease.
Pathological findings in nerve and muscle biopsies from 55 women with breast implants were reported in an abstract by Vogel and Edmondson (1996). Biopsies were examined by light and electron microscopy and by teasing the nerve fibers. Pathology was observed in 6 of 55 biopsies, including 3 with axonal neuropathy, 1 with granulomatous neuritis and myositis, 1 with chronic inflammatory demyelinating polyneuropathy (CIDP), and I with Charcot-Marie-Tooth disease. The authors concluded that only conventional neuromuscular disease was found in these women (Vogel and Edmondson, 1996).
Additional pathological and toxicological reports are reviewed in Chapter 4. Hine et al. (1969) did not find evidence for neurotoxicity on injection of silicone syringe lubricant into the lumbar subdural space and cisterna magna of rabbits, monkeys, and rats. Silicone was implanted subdurally in the brain of rats with no observable effect (Agnew et al., 1962). No direct evidence of silicone gel toxicity to peripheral nerves was