Natural history of upper cervical lesions in rheumatoid arthritis.

The natural history of the upper cervical lesions in rheumatoid arthritis (RA) was investigated, based on a follow-up study of 79 patients. At the beginning of this study, anterior atlantoaxial subluxation (AAS) was found in 35 patients, AAS combined with vertical subluxation (VS) in 34, and VS alone in 10. During the follow-up period (mean, 6.4 years), these lesions deteriorated in 30 of the 79 patients. To evaluate the occipitoatlantoaxial relation, the angles between occiput and atlas (C0/C1 angle) and between atlas and axis (C1/C2 angle) were measured, and the correlation between these angles and deterioration of the lesions was investigated. The severity of RA was classified according to the "disease subset" advocated by one of us (T.O.): the least erosive subset (LES), the more erosive subset (MES), and the mutilating subset (MUD). There was a significant positive correlation between the C1/C2 angle and atlantodental interval (ADI) and a significant negative correlation between the C0/C1 angle and the ADI. This indicates that the atlas not only shifts forward but also slips down and forward at an incline from the axis. With an increase of the atlantal inclination, the anterior arch of atlas displaces in an anteroinferior direction, and VS combines with AAS. The development of associated VS lessens the amount of the ADI. At the advanced stage of the natural course, AAS is concealed, and VS alone is demonstrated. We concluded that the upper cervical lesion deteriorated in the order of AAS, AAS + VS, and VS alone. In patients classified as the LES subset, only AAS was found, and VS was never combined with AAS at the terminal stage. In patients in the MES, VS frequently combined with AAS. All patients who deteriorated to VS alone were ranked as MUD.