Familial risks for nerve, nerve root and plexus disorders in siblings based on hospitalisations in Sweden

Background: Nerve, nerve root and plexus disorders are common diseases, but little is known about familial clustering in these diseases. This is, to our knowledge, the first systematic family study carried out on these diseases. Methods: Familial risks for siblings who were hospitalised for nerve, nerve root and plexus disorders in Sweden were defined. A nationwide database for neurological diseases was constructed by linking the Multigeneration Register on 0-69-year-old siblings to the Hospital Discharge Register covering the years 1987-2001. Standardised risk ratios (SIRs) were calculated for affected sibling pairs by comparing them with those whose siblings had no neurological disease. Results: 29 686 patients, 43% men and 57% women, were diagnosed at a mean age of 37.5 years. 191 siblings were hospitalised for these disorders, giving an overall SIR of 2.59 (95% CI 1.58 to 4.22), with no sex difference. Plantar nerve mononeuritis and carpal tunnel syndrome showed the highest familial risks: 4.82 (1.08 to 16.04) and 4.08 (2.07 to 7.84), respectively. Lateral poplitean and plantar nerve neuritis preferentially affected women, with SIRs of >8; disorders of the other cranial nerves affected only men, with an SIR of >10. Concordant trigeminal neuralgia, Bell's palsy and carpal tunnel syndrome showed familial risks, but, with the exception of Bell's palsy, they also showed correlation between spouses, implying environmental sharing of risk factors. Conclusions: The results cannot distinguish between inheritable or shared environmental factors, or their interactions, but they clearly show familial clustering, suggestive of multifactorial aetiology and inviting for aetiological research.