Sixth Cranial Nerve Involvement in Early Onset Krabbe Disease

A 5-month-old infant developed generalized hypotonia, spasticity, and feeding difficulties, and presented severe hypertonia of the four limbs and inability to control head posture. Brain magnetic resonance imaging showed a confluent pattern of T2 signal hyperintensity involving both centrum semiovale, the posterior limb of the internal capsules, the bulbar pyramids, and the dentate nuclei ([Fig. 1]). The thalami presented low signal intensity on T2-weighted imaging. Enhancement of the oculomotor (cranial nerve [CN] III), trigeminal (CN V), and abducens (CN VI) nerves—through their cisternal segments—was also demonstrated ([Fig. 2]). Deficient enzymatic activity of galactocerebrosidase was found on total leukocytes, and genetic testing detected a composite heterozygosity of the genetic variants c.884A > T(p.N295I) and c.1162-?_*1718 + ?del(del30kb), prompting the diagnosis of Krabbe disease.

Fig. 1 Axial T2-weighted image at the (A) centrum semiovale, (B) basal ganglia, and (C) cerebellar levels, demonstrates a confluent pattern of signal hyperintensity involving both centrum semiovale, the posterior limb of the internal capsules, as well as the bulbar pyramids and dentate nuclei. At the basal ganglia level (B) low signal intensity of the thalami is also depicted.

Fig. 2 Axial T1-weighted image postgadolinium shows bilateral cranial nerve (CN) III (A), and CN V (B) enhancement, as well as thickening of the prechiasmatic segment of both optic nerves (A). CN VI enhancement can be depicted on axial (C, arrows), coronal (D, arrows), and parasagittal (E, arrow) T1-weighted images postgadolinium.

Among leukodystrophies, multiple cranial nerve enhancement may be found on early onset Krabbe disease and metachromatic leukodystrophy[1] [2] [3] [4] [5]; the mechanism responsible for this finding is still unclear, but it is probably related to demyelination and low-grade inflammation similar to that seen in peripheral nerves.[2] [3] The finding of multiple cranial nerve enhancement, including CN VI involvement, adds specificity in the diagnosis of these entities, prompting an appropriate laboratory differential, and, in selected cases, referral for stem cell transplantation.[3]

• References

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