Thalamic T2 hypointensity: a diagnostic clue for Tay–Sachs disease

Excerpt

A 15-month-old male infant was admitted to our clinic due to complaints of hyperirritability that had persisted since he was 6 months old. The infant exhibited axial hypotonia, visual fixation, and tracking, as well as very limited spontaneous movements, and no head control. Tendon reflexes were to elicit. The patient was unable to exhibit head control since he was 4 months of age, and required support when sitting until 10 months of age. Brain magnetic resonance imaging (MRI) revealed a bilateral low intensity signal in the thalamus, and a bilateral moderately high intensity signal in the white matter and basal nuclei (Fig. 1a–c). In control MRI of the patient when compared to normal patients at the same age, T2 hypointensity became evident in thalamus (Figs. 2, 3). Serum was also analyzed for hexosaminidase A by a fluorometric method defined by O’Brien et al. [1]. According to laboratory tests, the patient’s leukocyte Beta-hexosaminidase A activity was 30.1 nmol/mg protein/h (control range = 153–371 nmol/mg protein/h), while the total leukocyte Beta-hexosaminidase activity was 1240.1 nmol/mg protein/h (control range = 734–1628 nmol/mg protein/h) and leukocyte beta-hexosaminidase A activity was 2.4 % of total hexosaminidase (normal value: 63–75 %). Based on these values, Tay–Sachs disease was diagnosed. Tay–Sachs disease, which also known as GM2 gangliosidosis, is disorder that results from hexosaminidase A deficiency. The disease, which shows early onset in infancy, is characterized by macrocephaly, convulsions, hypersensitivity to sound, and bilateral red spots on the eyes’ fundus. The main MRI findings in Tay–Sachs disease are bilateral high intensity signals on the T2 images of the patients’ cortex and basal ganglia. Over time, such signals are reported to evolve in the white matter of patients with this and related illnesses [2]. Bilateral T2 hypointensity at the thalamus is accepted as an indication of lysosomal storage diseases, and is observed in Tay–Sachs and Sandhoff diseases (GM2 gangliosidosis), Krabbe disease, metachromatic leukodystrophy (MLD), and neuronal ceroid lipofuscinosis (NCL) [3]. Fourteen types of NCL are available, and in types of infantile, late onset and juvenile NCL thalamic hypointensity can be visible on T2-weighted MRI images [4]. It is possible to clinically distinguish Tay–Sachs and Sandhoff disease based on the presence or absence of hepatosplenomegaly, since this condition is only observed in Sandhoff disease. A diagnosis of Sandhoff disease can be further confirmed by assay of beta-hexosaminidase activities; in this condition, there is deficiency of both the hexosaminidase A and B isozymes. NCL shows similar features to Tay–Sachs diseases, but is accompanied by severe cerebral atrophy. In Krabbe disease, the T2 hypointensity tends to be more extensive, affecting the cerebellum, central white matter, and basal ganglia, along with the thalamus [5]. Observation of T2 thalamic hypointensity is an important indication of lysosomal storage diseases, and assists in the diagnosis of various neurometabolic diseases of an inherited nature.

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