FDG PET/CT with SPM Analysis in Early Diagnosis of Clinically Suspected Osmotic Demyelination Syndrome with Non-contributory MRI

We report a case of 66 year old lady, known case of hypertension and type-2 diabetes mellitus, who developed stiffness of limbs with associated slurring of speech and gait imbalance, since 4 days. On biochemical analysis, she was found to have hyponatremia (serum sodium 95 mmol/l) and was started on 3% saline therapy, following which the serum sodium level rose up to 120 mmol/l in the next 36 hours. Although her general condition showed improvement, she had deterioration in speech and bulbar function. On central nervous system examination, she was conscious and had bilateral gaze-evoked nystagmus without any restriction in ocular movements. She had relatively poor bilateral palatal movement with power IV+/V, increased generalized tone and equivocal plantar response. Gait ataxia and limb incoordination was also present. Suspecting osmotic demyelination syndrome (ODS), MRI brain was done, which was found to be normal [Figure 1a–d]. Her blood investigations, electroencephalogram, and autoimmune panel came out to be noncontributory. Fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) whole-body scan was done to rule out any precipitating factor. FDG-PET/CT scan was done [Figure 2] which revealed hypermetabolism in the basal ganglia, thalamus, pons, and cerebellum with no obvious abnormality on the corresponding CT images, which was in favor of pontine and extrapontine myelinolysis. SPM analysis [Figure 3] was done to validate the findings of FDG-PET. She was managed conservatively with serum sodium and potassium monitoring to keep the sodium levels around 130–134 mmol/l. She responded to the therapeutic interventions and stabilized gradually. Repeat MRI done 2 weeks later showed T2 hyperintensity in the pons, basal ganglia, and thalami with signal alteration in pons on diffusion-weighted (DW) imaging 'suggestive of ODS' [Figure 1e–h].

Close

Figure 1 MRI scan showing T2-weighted and corresponding diffusion-weighted images. The images in the upper row (a-d) represent the initial MRI scan done at the time of presentation of symptoms of osmotic demyelination syndrome, which was unremarkable. Follow-up MRI (e-h) done 2 weeks after the initial MRI scan shows subtle hyperintensity in the basal ganglia, thalamus, and pons with restricted diffusion in the pons, consistent with the diagnosis of osmotic demyelination syndrome

Export to PPT

Close

Figure 2 Fused axial FDG PET/CT images (a-c) showing hypermetabolism in the pons, basal ganglia, thalamus, and cerebellum with no obvious abnormality on the CT scan

Export to PPT

Close

Figure 3 SPM analysis image showing areas of hyper-metabolism co-registered to a normal T1 weighted MRI for localization of region of involvement

Export to PPT

ODS, which encompasses both central and extrapontine myelinolysis, is a rare neurological complication attributed to rapid correction of hyponatremia or rapid shifts of osmolality in certain metabolic and toxic states.[1] It is characterized by destruction of the myelin sheath and oligodendrocytes in the pons, cerebellum, hippocampus, basal ganglia, brainstem, and thalamus without any inflammation with relative preservation of the axons.[1] The diagnosis is usually based on clinical suspicion and confirmed on MRI. Conventional MRI including T1-weighted, T2-weighted, fluid-attenuated inversion recovery (FLAIR), and DW imaging may show lesions in the form of signal alteration, days to weeks after the onset of symptoms, and may not be contributory to the diagnosis during the initial period.[234] FDG, a competitive glucose analog, demonstrates glucose metabolic activity at a given physiological or pathological site. Activated microglia and astrocytes in the brain, with their phagocytic properties, accumulate very rapidly at the site of demyelination in ODS and show increased glycolysis secondary to their accumulation; this results in focal hypermetabolism on FDG-PET images.[5] In our patient, in the clinical setting of complaints of dysarthria and ataxia with bulbar dysfunction and altered sensorium, in the background of rapid correction of hyponatremia, led to a clinical suspicion of ODS, which was strongly supported by the presence of focal hypermetabolism in pons and multiple extrapontine regions on FDG-PET/CT scan.[5] Thus, an FDG-PET/CT scan may act as a noninvasive confirmatory modality and contribute to the early diagnosis and management of patients with clinical suspicion of ODS and noncontributory/normal MRI.