Abstract
Background SOD1 mutations are the second most commonly implicated genetic cause of ALS. Many SOD1 variants have been identified, with few known to be linked to a defined clinical phenotype. 88% of patients with mutations in SOD1 are diagnosed with limb-onset disease. Only 2% of SOD1 patients are diagnosed with bulbar onset disease, which usually confers a significantly poorer prognosis.
Isolated bulbar palsy is a rare variant of ALS, characterised by symptoms confined to the bulbar region for a prolonged period of time, with relative sparing of the limbs. It comparatively confers a significantly better prognosis.
We describe a case of isolated bulbar palsy in a patient with ALS due to a SOD1 mutation (A-G, H43R).
Cases After initial presentation with mild dysarthria and hypophonia, a 36 year-old female was diagnosed with ALS. Her condition remained isolated until 4 years into her disease, when she noticed mild impairment of dexterity in her upper limbs. She remains asymptomatic from a respiratory perspective, and her weight has been stable, without dysphagia since her initial diagnosis with ALS.
At the most recent review 14 years post-diagnosis, there was mild to moderate dysarthria with hypophonia. Limb examination revealed mild weakness of her upper limbs, in a distal pattern.
Discussion ALS is a heterogeneous disease. While ALS represents a universally fatal condition, with a typical lifespan of 2–3 years, rare SOD1 variants may exhibit unexpected disease trajectories, which may confound approaches in the advent of antisense oligonucleotide therapy.
