Case Study: Late-Onset Huntington’s Presents Like Parkinson’s Disease

Man, 56, showed Parkinson's-like symptoms at diagnosis

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by Steve Bryson, PhD |

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A 56-year-old man with undiagnosed late-onset Huntington’s disease presented with Parkinson’s disease-like symptoms, including bradykinesia, or slowness of movement, a case study reported.

He was correctly diagnosed after clinicians learned of a family history of Huntington’s and ordered genetic testing.

Given the diagnosis, the researchers recommended that Huntington’s disease be considered when older patients with a family history of Huntington’s show Parkinson’s-like symptoms.

“Some patients can initially present atypical movements other than the usual symptoms, such as parkinsonism, ataxia [poor muscle control], and dystonia [involuntary muscle contractions],” the team wrote.

The case study, “Atypical parkinsonism can be a presenting feature of late-onset Huntington’s disease,” was published in the journal Clinical Case Reports.

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Huntington’s disease vs Parkinson’s: similar symptoms

Huntington’s disease is caused by defects in the huntingtin (HTT) gene. These mutations lead to an expansion of CAG nucleotides, which are building blocks of DNA. Typically, the HTT gene CAG expansion contains 10 to 35 repeats, but in people with Huntington’s disease, it may be repeated from 36 to more than 120 times.

These genetic defects lead to an imbalance in dopamine levels in the brain. Dopamine is a neurotransmitter, or nerve cell signaling molecule, that plays an essential role in body movements.

Unusually high dopamine levels are thought to cause chorea — abrupt movements that are irregular and unpredictable. In the later stages of the disease, dopamine levels can drop, which can ease chorea but then show symptoms similar to Parkinson’s disease, a movement disorder characterized by abnormally low dopamine levels. This can often lead to a misdiagnosis.

Now, researchers based at the Shahid Beheshti University of Medical Science, in Iran, described the case of a man in his mid-50s with undiagnosed Huntington’s who was treated for Parkinson’s-like symptoms.

The man had undergone treatment for depression for eight years before gradually developing other symptoms that all appeared to be signs of Parkinson’s disease. These symptoms included speech impairment, walking difficulties, an urgent need to urinate, constipation, memory problems, and frequent falling.

His medical records showed no history of brain inflammation, known as encephalitis, or exposure to toxic substances. Nor had the man received medications designed to lower dopamine or block dopamine receptors.

Notably, his now-deceased father had Huntington’s disease, as did his sister, who carried 42 CAG repeats.

On examination, the patient had an expressionless face and eye movements that were slow in all directions but more prominent vertically. His upper and lower extremities were rigid, and he showed slowness of movement, called bradykinesia, also consistent with Parkinson’s.

During the exam, he showed repetitive hand movements and could not stand for more than three minutes to measure blood pressure. His speech was unclear, high-pitched, and whiny, and he also had significant cognitive impairment.

MRI scans demonstrated generalized atrophy, or shrinkage of the brain, which was more prominent in the temporal lobes and caudate nucleus. That area of the brain typically has the heaviest nerve damage in Huntington’s.

Because of his family history of Huntington’s, he underwent genetic testing, which demonstrated 39 CAG repeats in the HTT gene.

He had been treated with medications for dementia (donepezil), to control body movements (amantadine, sold as Gocovri), and to prevent seizures (valproate sodium).

The team added the standard Parkinson’s therapy levodopa; a precursor molecule converted to dopamine in the brain. The dose was gradually increased from 25 mg three times per day to 100 mg three times daily, and amantadine also was increased.

Treatment led to mild improvement in bradykinesia, rigidity, and gait.

The researchers noted that this was the fifth reported case of late-onset Huntington’s that presented with Parkinson’s-like symptoms.

Huntington’s disease “should be considered as a differential diagnosis of patients with atypical parkinsonism, especially if family history is positive,” the researchers concluded.