Hypertrophic olivary degeneration

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Hypertrophic olivary degeneration (HOD) is a rare condition characterised by a unique pattern of trans-synaptic degeneration. It is caused by a lesion in the triangle of Guillain and Mollaret, resulting in hypertrophy of the inferior olivary nucleus. The three corners of the triangle are:

Clinical presentation

~~Pathology in dentato-rubro-olivary pathway with resultant disinhibition~~Oculopalatal tremor is a distinctive part of the ~~inferior~~presentation of hypertrophic olivary ~~nucleus~~degeneration, although is ~~further modulated by the cerebellum~~also seen in many other brainstem and ~~can manifest as oculopalatal~~cerebellar conditions ⁴. Oculopalatal tremor comprises ocular, palatal and other muscular involuntary movements.

~~Palatal~~

palatal myoclonus, rhythmic involuntary movement of the soft palate, uvula, pharynx, larynx and upper extremity are classically described clinical features.~~Palatal~~
palatal myoclonus may not always be present, but when it is present, it is pathognomonic. ~~Ocular tremor presents as~~
oscillopsia may be present due to the pendular nystagmus. caused by the ocular tremor ⁴

Pathology

The connection between the red nucleus, ipsilateral inferior olivary nucleus and the contralateral dentate nucleus forms the triangle of Guillain and Mollaret. Interruption of either connection between the dentate nucleus and contralateral red nucleus (dentatorubral tract, superior cerebellar peduncle) or the connection between the red nucleus and ipsilateral inferior olivary nucleus (central tegmental tract) leads to changes in the olive. The olive receives inhibitory (GABAergic) signals within the dentato-rubro-olivary pathway, with ~~trans-neuronal~~transneuronal degeneration causing enlargement rather than atrophy.

Pathologically, this is characterised by "trans-synaptic degeneration resulting in vacuolation of the neurons" and an increase in astrocytes. Isolated lesions of the inferior cerebellar peduncle do not cause hypertrophic olivary degeneration, as anatomically there are no direct connections between the inferior olivary nucleus and the contralateral dentate nucleus (fibres from the inferior olivary nucleus project to the cerebellar cortex via the olivocerebellar tracts and then to the dentate nucleus).

Oculopalatal tremor results from disinhibition of the inferior olivary nucleus, following the pathology in dentato-rubro-olivary pathway which is further modulated by the cerebellum ⁴.

Radiographic features

It is often seen several months after the original insult.

MRI

The inferior olivary nucleus gets larger and increases in signal intensity on T2 weighted and T2-FLAIR sequences.

Typically, within a few months, T2 signal increases and lasts for 3-4 years, whereas hypertrophy occurs later (at about one year), and resolves by 3-4 years. There are three stages:

T2 hyperintense without olivary swelling
T2 hyperintense and olivary swelling occur concomitantly, developing after 6 months and persisting for nearly 3-4 years
olivary swelling subsides, but T2 hyperintensity persists

Differential diagnosis

General imaging differential considerations include:

infarction
demyelination
astrocytoma
metastases
lymphoma
infection, including tuberculosis

-</ul><h4>Clinical presentation</h4><p>Pathology in dentato-rubro-olivary pathway with resultant disinhibition of the inferior olivary nucleus is further modulated by the cerebellum and can manifest as oculopalatal tremor.</p><p>Palatal myoclonus, rhythmic involuntary movement of the soft palate, uvula, pharynx, larynx and upper extremity are classically described clinical features.</p><p>Palatal myoclonus may not always be present, but when it is present, it is pathognomonic. </p><p>Ocular tremor presents as pendular nystagmus.</p><h4>Pathology</h4><p>The connection between the red nucleus, ipsilateral inferior olivary nucleus and the contralateral dentate nucleus forms the triangle of Guillain and Mollaret. Interruption of either connection between the dentate nucleus and contralateral red nucleus (<a href="/articles/dentatorubral-tract">dentatorubral tract</a>, <a href="/articles/superior-cerebellar-peduncle-1">superior cerebellar peduncle</a>) or the connection between the red nucleus and ipsilateral inferior olivary nucleus (central <a href="/articles/tegmental-tract">tegmental tract</a>) leads to changes in the <a href="/articles/olive">olive</a>. The olive receives inhibitory (GABAergic) signals within the dentato-rubro-olivary pathway, with trans-neuronal degeneration causing enlargement rather than atrophy. </p><p>Pathologically, this is characterised by "trans-synaptic degeneration resulting in vacuolation of the neurons" and an increase in astrocytes. Isolated lesions of the inferior cerebellar peduncle do not cause hypertrophic olivary degeneration, as anatomically there are no direct connections between the inferior olivary nucleus and the contralateral dentate nucleus (fibres from the inferior olivary nucleus project to the cerebellar cortex via the <a href="/articles/olivocerebellar-tract">olivocerebellar tracts</a> and then to the dentate nucleus).</p><h4>Radiographic features</h4><p>It is often seen several months after the original insult.</p><h5>MRI</h5><p>The inferior olivary nucleus gets larger and increases in signal intensity on T2 weighted and T2-FLAIR sequences.</p><p>Typically, within a few months, T2 signal increases and lasts for 3-4 years, whereas hypertrophy occurs later (at about one year), and resolves by 3-4 years. There are three stages:</p><ol>
+</ul><h4>Clinical presentation</h4><p>Oculopalatal tremor is a distinctive part of the presentation of hypertrophic olivary degeneration, although is also seen in many other brainstem and cerebellar conditions <sup>4</sup>. Oculopalatal tremor comprises ocular, palatal and other muscular involuntary movements.</p><ul>
+<li>palatal myoclonus, rhythmic involuntary movement of the soft palate, uvula, pharynx, larynx and upper extremity are classically described clinical features</li>
+<li>palatal myoclonus may not always be present, but when it is present, it is <a title="Pathognomonic" href="/articles/pathognomonic">pathognomonic</a>
+</li>
+<li>
+<a title="Oscillopsia" href="/articles/oscillopsia">oscillopsia</a> may be present due to the pendular nystagmus caused by the ocular tremor <sup>4</sup>
+</li>
+</ul><h4>Pathology</h4><p>The connection between the red nucleus, ipsilateral inferior olivary nucleus and the contralateral dentate nucleus forms the triangle of Guillain and Mollaret. Interruption of either connection between the dentate nucleus and contralateral red nucleus (<a href="/articles/dentatorubral-tract">dentatorubral tract</a>, <a href="/articles/superior-cerebellar-peduncle-1">superior cerebellar peduncle</a>) or the connection between the red nucleus and ipsilateral inferior olivary nucleus (central <a href="/articles/tegmental-tract">tegmental tract</a>) leads to changes in the <a href="/articles/olive">olive</a>. The olive receives inhibitory (GABAergic) signals within the dentato-rubro-olivary pathway, with transneuronal degeneration causing enlargement rather than atrophy. </p><p>Pathologically, this is characterised by "trans-synaptic degeneration resulting in vacuolation of the neurons" and an increase in astrocytes. Isolated lesions of the inferior cerebellar peduncle do not cause hypertrophic olivary degeneration, as anatomically there are no direct connections between the inferior olivary nucleus and the contralateral dentate nucleus (fibres from the inferior olivary nucleus project to the cerebellar cortex via the <a href="/articles/olivocerebellar-tract">olivocerebellar tracts</a> and then to the dentate nucleus). </p><p>Oculopalatal tremor results from disinhibition of the inferior olivary nucleus, following the pathology in dentato-rubro-olivary pathway which is further modulated by the cerebellum <sup>4</sup>. </p><h4>Radiographic features</h4><p>It is often seen several months after the original insult.</p><h5>MRI</h5><p>The inferior olivary nucleus gets larger and increases in signal intensity on T2 weighted and T2-FLAIR sequences.</p><p>Typically, within a few months, T2 signal increases and lasts for 3-4 years, whereas hypertrophy occurs later (at about one year), and resolves by 3-4 years. There are three stages:</p><ol>

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