Hippocampal atrophy detected by volumetric MRI is a sensitive feature of early Alzheimer's disease (AD), but there are no studies evaluating hippocampal atrophy by MR volumetry in other dementing diseases. We therefore compared hippocampal volumes in a total of 113 subjects: 50 patients with mild to moderate AD, 9 patients with vascular dementia (VaD), 12 patients with idiopathic Parkinson's disease (PD) without dementia, 8 patients with PD and dementia (PDD), and 34 elderly control subjects. Thin, coronal, contiguous images were obtained by a 1.5-T MR imager. All patient groups had significantly smaller volumes of the hippocampus compared with the control group. In the PDD group, the absolute volumes were even smaller than in the AD group. In the PD group, the volumes were diminished to a lesser but significant extent. The volumes in the VaD group varied: of nine patients, two had no atrophy, three had unilateral, and four had bilateral atrophy. We postulate that hippocampal atrophy does not seem to be a specific phenomenon of dementia in AD but also occurs in VaD and PDD, and even in PD when no dementia is present. However, coexistence of AD pathology in our PD and VaD patients cannot be ruled out. Further studies with access to neuropathologic data are needed.

In patients with cryptogenic epilepsy, recurrent seizures may cause damage to the hippocampus throughout the lifetime of the patient.

References1. Levin MJ, Gardner P, Waldvogel F. "Tropical" pyomyositis, an unusual infection due to Staphylococcus aureus. N Engl J Med 1971;284:196-198. 2. Back SA, O'Neill T, Fishbein G, Gwinup G. A case of group B streptococcal pyomyositis. Rev Infect Dis 1990;12784-787. 3. Mustafa MM, Scarvey L, Rollins N, Siege1 JD. Primary suppurative myositis associated with HaemophiEus influenzae type B septicemia. Pediatr Infect Dis J 1988;7:815-817. 4. Solbrig MV, Sher JH, Kula RW. Rhabdomyolysis in leptospirosis (Weil's disease). J Infect Dis 1987;156:692-693. 5. Adamski GB, Garin EH, Ballinger WE, Shulman ST. Generalized nonsuppurative myositis with staphylococcal septicemia. J Pediatr 1980;96694-697. 6. Lannigan R, Austin TW, Vestrup J. Myositis and rhabdomyolysis due to Staphylococcus aureus septicemia. J Infect Dis 1984;150:784. 7. Felice K, DeGirolami U, Chad DA. Pyomyositis presenting as rapidly progressive generalized weakness. Neurology 1991;41:944-945.

We analyzed hippocampal volumes and T2 relaxation times by MRI from 78 control subjects, 24 patients with temporal lobe epilepsy, and 55 patients with Alzheimer's disease (AD). In the epilepsy group, the hippocampal volumes were 27% smaller than in control subjects (p < 0.001). The T2 relaxation times were prolonged (8 to 20 ms compared with control subjects) in the head, body, and tail portions of the hippocampus on the focal side (p < 0.01) and also on the contralateral side (p < 0.05) compared with control subjects. In the epilepsy group, the prolongation of T2 relaxation time correlated inversely with the hippocampal volume (p < 0.05). In the AD group, the hippocampal volumes were 35% smaller than in control subjects (p < 0.01). The T2 relaxation times were slightly prolonged (5 to 6 ms) in the head and tail portions of the right hippocampus (p < 0.01), but the T2 relaxation times did not correlate with the hippocampal volumes. These data show that the degree of prolongation of T2 relaxation time is associated with severity of hippocampal atrophy in temporal lobe epilepsy but not in AD.

We investigated the effects of estrogen replacement therapy on water maze non-spatial and spatial navigation in mice. Three groups of mice were ovariectomized and two of these groups being implanted with s.c. pellets that produce blood levels of estrogen close to those found in estrous (estrogen low, 75-100 pg/ml blood) or proestrous (estrogen high, 300-400 pg/ml). The behavioral assessment was initiated 7 days after pellet implantation. Non-spatial navigation to a clearly visible platform was stimulated by low and high levels of estrogen. However, spatial navigation to a hidden platform was improved by low estrogen levels. We found that estrogen improves two different types of memory processes that depend on striatal (non-spatial navigation) and hippocampal (spatial) memory systems.