This chapter considers the often difficult diagnosis of neurosarcoidosis, its prevalence, pathology, differential diagnosis, treatment and prognosis. Although advances in imaging techniques have alerted clinicians to this potential diagnosis more frequently than in the past, there is still no definitive non-invasive investigation to provide certain confirmation of clinical suspicion. The diagnosis is one which should always be treated with a healthy degree of scepticism, as even typical granulomas may have alternative causes.
Prevalence rates for intrathoracic sarcoidosis vary from greater than 50 per 100000, for example in African– Americans and Irish, to under 10 per 100000 (James & Hosoda, 1994). Much higher prevalence rates were obtained when consecutive postmortems were performed on approximately 60% of all deaths in an area of Sweden, when evidence of sarcoidosis was found in 43 individuals, only three of whom were known to have sarcoidosis during life, yielding a prevalence of 641 per 100000 (Hagerstrand & Linel, 1964). The clinical significance of these findings is uncertain, but they suggest that the pathological process is far commoner than we recognize, although this may be limited to subclinical disease in most cases. Intermediate estimates for the prevalence of systemic sarcoidosis of 10–20 per 100000 are likely for caucasians in London and New York.
Previous data from large series of patients with sarcoidosis have estimated that approximately 5% of such patients will have clinical involvement of the nervous system (Maycock et al., 1963; Stilzbach et al., 1974; Delaney, 1977; Stern et al., 1985), although postmortem studies suggest that antemortem diagnosis is only made in 50% with nervous system involvement (Iwai et al., 1993). Conservatively, we can therefore estimate that about 5 to 10 patients per million population will have clinical neurosarcoidosis, although this figure will vary according to local prevalence rates.
Clinical aspects of neurosarcoidosis
As with any rare disease, information concerning natural history, prognosis and treatment strategies is seldom based on large prospective cohort analysis, let alone on randomized trials.
Because nervous system sarcoidosis is relatively rare, few large series exist in the literature; the largest has been a British series of 68 patients (Zajicek et al., 1999).