Objective: We present a case of late onset task specific segmental (cervico-lingual) dystonia misdiagnosed as bulbar myasthenia gravis.

Background: Muscle diseases have been previously reported to mimic movement disorders such as bent spine syndrome caused by FSHD misdiagnosed as dystonic camptocormia or head drop mimicking the antecollis of MSA or Parkinson’s disease. The diagnosis of a movement disorder is more rarely made in a patient with presumed neuromuscular disease.

Method: A 67-year-old female presented with a two-year history of difficulty with speech and head drop. She reported that her speech would get heavy and effortful particularly when talking for long periods of time. She was investigated for presumed myasthenia gravis and started on treatment given the bulbar onset.

Results: Clinical assessment by a Neuromuscular specialist revealed a lack of clear neck flexion or bulbar weakness. Speech was normal for single words but talking in sentences revealed altered speech production with tongue protrusion and anterocaput posturing. The patient was noted to use her hand to hold up her chin while talking, demonstrating a geste antagoniste. Mild blepharospasm was also noted during prolonged speech.

A diagnosis of task-specific cervico-lingual dystonia was made and treatments for myasthenia gravis were weaned. The patient was commenced on Trihexyphenidyl to modest response. Exploration of customised devices utilising her geste antagoniste is underway ahead of consideration of botulinum toxin therapy which may prove difficult in its delivery in this complex case.

Conclusion: Careful clinical assessment of patients is a key component of neurological diagnosis and a systematic approach is important in classification of movement disorders. This case report highlights how the task-specific element of a dystonia can be misdiagnosed as fatiguable weakness.

References: 1. Kim & Kim (2019), ‘Task-specific oromandibular dystonia in a telemarketer’, Journal of Movement Disorders, 12(2): 125-127.
2. Prasad et. al (2017), ‘Speech induced cervical dystonia: an unusual task specific dystonia’, Parkinsonism & Related Disorders, 14(1): 84-85.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/an-uncommon-task-specific-dystonia-masquerading-as-myasthenia-gravis/