Amyloid vs FDG-PET in the differential diagnosis of AD and FTLD

OBJECTIVE

To compare the diagnostic performance of PET with the amyloid ligand Pittsburgh compound B (PiB-PET) to fluorodeoxyglucose (FDG-PET) in discriminating between Alzheimer disease (AD) and frontotemporal lobar degeneration (FTLD).

METHODS

Patients meeting clinical criteria for AD (n = 62) and FTLD (n = 45) underwent PiB and FDG-PET. PiB scans were classified as positive or negative by 2 visual raters blinded to clinical diagnosis, and using a quantitative threshold derived from controls (n = 25). FDG scans were visually rated as consistent with AD or FTLD, and quantitatively classified based on the region of lowest metabolism relative to controls.

RESULTS

PiB visual reads had a higher sensitivity for AD (89.5% average between raters) than FDG visual reads (77.5%) with similar specificity (PiB 83%, FDG 84%). When scans were classified quantitatively, PiB had higher sensitivity (89% vs 73%) while FDG had higher specificity (83% vs 98%). On receiver operating characteristic analysis, areas under the curve for PiB (0.888) and FDG (0.910) were similar. Interrater agreement was higher for PiB (κ = 0.96) than FDG (κ = 0.72), as was agreement between visual and quantitative classification (PiB κ = 0.88-0.92; FDG κ = 0.64-0.68). In patients with known histopathology, overall classification accuracy (2 visual and 1 quantitative classification per patient) was 97% for PiB (n = 12 patients) and 87% for FDG (n = 10).

CONCLUSIONS

PiB and FDG showed similar accuracy in discriminating AD and FTLD. PiB was more sensitive when interpreted qualitatively or quantitatively. FDG was more specific, but only when scans were classified quantitatively. PiB slightly outperformed FDG in patients with known histopathology.

Distinct clinical and metabolic deficits in PCA and AD are not related to amyloid distribution

BACKGROUND/OBJECTIVE

Patients with posterior cortical atrophy (PCA) often have Alzheimer disease (AD) at autopsy, yet are cognitively and anatomically distinct from patients with clinical AD. We sought to compare the distribution of β-amyloid and glucose metabolism in PCA and AD in vivo using Pittsburgh compound B (PiB) and FDG-PET.

METHODS

Patients with PCA (n = 12, age 57.5 ± 7.4, Mini-Mental State Examination [MMSE] 22.2 ± 5.1), AD (n = 14, age 58.8 ± 9.6, MMSE 23.8 ± 6.7), and cognitively normal controls (NC, n = 30, age 73.6 ± 6.4) underwent PiB and FDG-PET. Group differences in PiB distribution volume ratios (DVR, cerebellar reference) and FDG uptake (pons-averaged) were assessed on a voxel-wise basis and by comparing binding in regions of interest (ROIs).

RESULTS

Compared to NC, both patients with AD and patients with PCA showed diffuse PiB uptake throughout frontal, temporoparietal, and occipital cortex (p < 0.0001). There were no regional differences in PiB binding between PCA and AD even after correcting for atrophy. FDG patterns in PCA and AD were distinct: while both groups showed hypometabolism compared to NC in temporoparietal cortex and precuneus/posterior cingulate, patients with PCA further showed hypometabolism in inferior occipitotemporal cortex compared to both NC and patients with AD (p < 0.05). Patients with AD did not show areas of relative hypometabolism compared to PCA.

CONCLUSIONS

Fibrillar amyloid deposition in PCA is diffuse and similar to AD, while glucose hypometabolism extends more posteriorly into occipital cortex. Further studies are needed to determine the mechanisms of selective network degeneration in focal variants of AD.

Noma in a full-term neonate

Noma is an uncommon gangrenous process usually affecting malnourished children. A full-term neonate with orofacial noma, bilateral choanal atresia, and transient neutropenia with B cell deficiency is reported. This unusual appearance of noma in a well-nourished newborn might be related to the combination of choanal atresia and transient immune deficiency.

Levan-induced glomerulitis in rabbits: a possible role for direct complement activation in situ

Since high-molecular-weight levan is known to reduce capillary permeability to large molecules, an experiment was designed to investigate whether this agent may attenuate the glomerulonephritis associated with acute serum sickness in rabbits. The study, in fact, demonstrated an enhancing effect of levan, which caused increased glomerular proliferative changes and leucocyte infiltration and, possibly, increased IgG deposition in this experimental model. In addition, rabbits injected only with levan also demonstrated mild glomerulitis and C3 deposition. In one of four rabbits examined, this was accompanied by a marked fall in the serum level of total haemolysing complement. Levan was demonstrated to cause activation of complement when incubated with normal rabbit serum in vitro. We believe that these findings are best explained on the basis of complement activation in situ by levan in the glomeruli, probably via the alternative pathway, with the resulting inflammatory response. In the case of BSA-injected rabbits, this response is believed to be additive to that of the classical immune complex-mediated complement activation.

Parathyroid hormone secretion and responsiveness to parathyroid hormone in primary hypomagnesemia

Parathyroid function was studied in two infant sisters with primary hypomagnesemia while they were both hypomagnesemic and hypocalcemic. In one of the infants, plasma immunoreactive parathyroid hormone (iPTH) was elevated, the calcemic response to exogenous parathyroid hormone (PTH) was absent, and the phosphaturic response was normal. Restoration of serum magnesium with i.v. magnesium corrected the hypocalcemia, with no further rise of plasma iPTH. In the other infant, plasma iPTH was undetectable, and exogenous PTH produced both phosphaturic and calcemic responses. Normalization of serum magnesium with i.v. magnesium resulted in a prompt release of endogenous PTH and correction of the hypocalcemia. These findings suggest that, in the first patient, hypocalcemia was associated with lack of response of the bone to both endogenous and exogenous PTH, while in the second patient, hypocalcemia was associated with inhibition of PTH release and a normal calcemic response to exogenous PTH. The factors that determine whether magnesium deficiency will result in inhibition of PTH release, in a lack of response of the bone to endogenous and exogenous PTH, or both, remain to be clarified.

Production of the hydroxylated metabolites of vitamin D in a neonate with a single hypoplastic-dysplastic kidney

The ability to produce dihydroxylated metabolites of vitamin D was studied in a term neonate suffering from severe renal insufficiency. The infant died at age 26 days owing to end-stage renal failure and the necropsy examination showed a single dysplastic kidney weighing 1.5 g. At age 2 weeks the serum levels of the dihydroxylated metabolites of vitamin D were found to be normal and a pronounced increase was noted 24 hours after injection of 100 000 IU vitamin D2. The study suggests that during the neonatal period a small renal mass is sufficient to maintain optimal circulating levels of the dihydroxylated metabolites of vitamin D.

Subcutaneous fat necrosis of the newborn

A case of subcutaneous fat necrosis of the newborn is described. Severe perinatal asphyxia preceded the appearance of the skin lesions. Premature rupture of membranes and the presence of foul-smelling meconium raised the possibility of infection by anaerobes as an additional etiologic factor. The main hypotheses concerning the cause and pathogenesis of this condition are reviewed. The alarming clinical picture that stands in sharp contrast to the benign prognosis is stressed.