Background: Subclinical multiple sclerosis (MS) has been identified incidentally at autopsy; apparently unaffected individuals with an affected twin have demonstrated magnetic resonance imaging (MRI) changes consistent with MS, and 'MRI relapses' are several times more common than clinical relapses.
Case description: A 39-year-old, right-handed man underwent MRI and PET scanning in 1986 as a 'normal' control in a Parkinson's disease study, where his father was the proband. MRI indicated multiple areas of abnormal signal intensity in a periventricular and grey-white matter junction distribution. Repeated clinical evaluations over the next 10 years were unchanged until 1996, when he complained of progressive weakness of the right foot and clumsiness in the right hand. MRI now indicated a further area of high signal intensity in the right posterior cord at the level of C5/C6. There was mild pyramidal distribution weakness in the right leg with an extensor plantar response on the same side. Over the next five years there has been mild progression in weakness and fatigue and intermittent Lhermitte's phenomenon. At no stage has there been a history of relapse, cerebrospinal fluid examination was normal and evoked responses (visual and somatosensory) are normal.
Conclusion: This case demonstrates the phenomenon of subclinical MS, unusually supported by prolonged clinical and MRI follow-up. The patient eventually became symptomatic nine years after MRI diagnosis and is following a primary progressive course. Although MRI is known to be sensitive in identifying subclinical 'attacks', the pattern illustrated here may actually be quite typical of primary progressive MS and is compatible with the later onset seen in this subgroup of patients.