A 68 year old hypertensive woman was referred to the neurology department having experienced a sudden weakness in mastication and mild dysarthria. When the patient was asked to protrude her tongue, a left lingual paresis became evident (fig 1); however, the tongue was normal while at rest in the mouth. Neurological examination was otherwise normal.

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Figure 1

 Left lingual paresis evident on tongue protrusion.

A brain computed tomogram gave evidence of a small haematoma limited to the posterior limb of the right internal capsule (fig 2). No other abnormal radiological findings were shown to be present on successive brain magnetic resonance imaging.

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Figure 2

 Haematoma visible in right internal capsule, CT scan.

Facial and lingual hemiparesis with mild limb involvement have been previously described in capsular genu syndrome, suggesting that motor corticopontine and corticocobulbar fibres are situated more in the genu of the internal capsule. Each hypoglossal nucleus receives impulses from both sides of the cortex but the genioglossus muscle probably has crossed unilateral innervation, thus an isolated right sided lesion of the upper motor neurone, in the internal capsule, is capable of causing lingual paresis that is evident only when the tongue is protruded. Differential diagnosis of sudden lingual hemiparesis, if unilateral, include lesions of the 12th nerve; atrophy and fasciculations of the tongue will also be present subsequently. This nerve can be damaged in the medulla (by conditions such as ischaemia or neoplasm) or after it leaves the brainstem and the skull through the hypoglossal foramen. Acute involvement of the hypoglossal nerve may arise with carotid dissection in the neck.

Sudden bilateral sopranuclear lingual paresis has been described with a bilateral cerebral infarction involving the anterior opercular region, and manifests itself in facial and pharyngeal diplegia.

The condition of this patient was unique because the lingual paresis manifested itself without having any association with other neurological findings and the lesion had occurred in the posterior limb of the internal capsule.