A Syndrome of Progressive Ataxia and Palatal Tremor (PAPT) in a Patient with Hypertrophic Olivary Degeneration

Sir,

Hypertrophic olivary degeneration (HOD) is a rare entity that shows trans-neuronal degeneration of the inferior olivary nucleus (ION). It can be idiopathic or symptomatic secondary to a structural lesion at Guillain–Mollaret triangle. This degeneration is unique in a way that it causes hypertrophy of ION rather than atrophy. A syndrome of progressive ataxia and palatal tremor (PAPT) is a much rarer degenerative disorder that is classified into familial and sporadic and is associated with bilateral HOD in magnetic resonance imaging (MRI) of almost all cases of PAPT.

A 49-year-old female with unremarkable past medical history presented with a 1-year history of slowly progressive gait unsteadiness associated with involuntary movements of the soft palate and eyes. She did not have any other neurological complaints and denied having ear click. Her family history was negative for a similar condition. Her neurological examination showed an alert, conscious and oriented patient with staccato speech and ataxic gait. Cranial nerves examination showed vertical pendular and horizontal gaze-evoked nystagmus and palatal tremor. Palatal tremor (PT) is shown in [Supplementary Video 1]. Cerebellar examination showed incoordination of movements of the upper and lower limbs with intention tremors. MRI of the brain showed abnormal nonenhancing hyperintense T2/FLAIR signal and bilateral hypertrophy of ION [Figure 1].

Figure 1.

MR imaging showing bilateral hypertrophic olivary degeneration; (a) T2-weighted, (b) FLAIR axial images through medulla showing hyperintensities in ION with mild hypertrophy and vacuolation on the left side. No cerebellar atrophy is present

Hypertrophic olivary degeneration is a rare condition characterized by a unique pattern of trans-neuronal degeneration. It is usually caused by a lesion in the Guillain–Mollaret triangle resulting in hypertrophy of the ION rather than atrophy. The main accepted explanation of hypertrophy is that HOD would develop due to a denervation process. Normal ION can generate spontaneous oscillations and a denervated ION is released from inhibitory inputs and would enlarge and develop sustained synchronized oscillations which the cerebellum accentuates resulting in abnormal motor output in the branchial arches.[1]

The trans-synaptic degeneration results in vacuolation of neurons, fibrillary gliosis, increase astrocytic number and size, and demyelination. Six phases of pathologic changes have been described in the following sequence: (1) No olivary change, (2) olivary amiculum degeneration, (3) olivary hypertrophy, (4) maximum olivary enlargement, (5) olivary pseudohypertrophy, and (6) olivary atrophy.[2]

The main clinical manifestation of HOD is PT, formerly called palatal myoclonus, affecting the soft palate, uvula, pharynx and larynx with or without ocular affection; oculo-palatal tremors (OPT). It can also involve other muscles from the branchial arches.[3]

There are two main conditions in which hypertrophic degeneration of the ION occurs. The most common etiology is following a structural brainstem or cerebellar lesion affecting Guillain–Mollaret pathway causing hypertrophy of the contralateral ION. A less common cause occurs without a structural lesion and is associated with PAPT. PAPT is considered as one of the causes of SPT and cases are classified into familial and sporadic. It is a rare distinct clinical entity which is reported in only few cases in literature with sporadic form being the most common. Features of sporadic PAPT include progressive ataxia, olivary degeneration, saccadic pursuit, hypermetric saccades, gaze-evoked nystagmus, vertical pendular nystagmus, INO, and absence of ear click.[4]

Hypertrophic olivary degeneration is present on MRI in almost all cases of PAPT with no structural lesion in the dentato–olivary pathway as described by Sperling and Herrmann[4] and later Samuel et al.[3]

Magnetic resonance imaging shows a characteristic nonenhancing hyperintense signal and enlargement of ION in T2/FLAIR sequences. However, not all PAPT have MRI findings as it depends on the stage of evolution of the degenerative process. On T2-weighted images, they characteristically go through three stages in the sequence of hyperintensity without hypertrophy, hyperintensity with hypertrophy followed by hyperintensity without hypertrophy again. Typically, within a few months, T2 signal increases and lasts for 3–4 years, whereas hypertrophy occurs later, at about 1 year, and resolves by 3–4 years.[5]

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient has given her consent for her images and other clinical information to be reported in the journal. The patient understands that her name and initials will not be published and due efforts will be made to conceal her identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.