Lingual Dysarthia

In last month’s challenge (available on PracticalNeurology.com),
we presented a case of a 70-year-old man with a sudden lisp.

Lingual dysarthria can be a feature of…

1. Myasthenia gravis (MG)
2. Amyotrophic lateral sclerosis (ALS)
3. Hypoglossal neuropathy
4. Hysteria
5. Lambert-Eaton myasthenic syndrome (LEMS)

   The answer is all of the above.

   • The tongue consists of four pairs of extrinsic and four pairs of intrinsic muscles. Tongue movement is served by the hypoglossal nerve.

   • Tongue weakness may present as dysarthria or inability to move food in the mouth properly. It is a feature of several neuromuscular disorders, including muscle diseases (polymyositis), nerve diseases (GBS), Neuromuscular junction (NMJ) disorders (MG, LEMS, Botulism), motor neuron disease (ALS, Kennedy’s disease), as well as mitochondrial disorders like Sensory Ataxia, Neuropathy Dysarthria, Ophthalmoplegia (SANDO).

   • Bulbar weakness without prominent ocular symptoms is not unusual in MG. As a matter of fact, it is a common manifestation of MuSK antibodies associated MG where atrophy of the tongue and face may lead to diagnostic confusion with bulbar onset ALS. Even tongue fasciculations are reported in MuSK antibodies associated MG.

   • Fatigability of dysarthria (worsening with speech) is more typically seen in MG.

   • In MG, the tip of the tongue is often affected early, leading to a “lisp,” as opposed to ALS, in which the bulk of the tongue is affected and leads to a “heavy tongue,” like the tongue of an intoxicated person.

   • Cerebellar dysarthria is irregular. The patient cannot count fast with regular intervals and consistent volume. n