Introduction Narcolepsy with cataplexy and myasthenia gravis are both chronic neurological conditions causing symptoms of muscle weakness, often affecting facial muscles, and both attributed to an immune-mediated aetiology. Here we report an adolescent girl diagnosed with both conditions and discuss possible shared mechanisms and the diagnostic challenges presented by her case, to inform and aid clinicians managing children and young people with these rare conditions.
Case A ten-year-old girl was referred o the paediatric sleep clinic with a two year history of excessive daytime sleepiness and cataplexy, featuring full loss of postural tone. She was subsequently found to have narcolepsy with cataplexy based on positive PSG (figure 1) & MSLT findings with supporting HLA-DQB1*06:02 result. She was managed with methylphenidate, and later venlafaxine, but experienced unsatisfactory symptom control.
Two years later she represented to ophthalmology with ptosis and was subsequently found to have elevated acetylcholine receptor antibodies. She was referred to paediatric neurology and clinical examination demonstrated fatiguability consistent with myasthenia gravis and pyridostigmine was started with good effect.
Discussion Interesting comparisons between both conditions can be drawn: both cause weakness that can affect facial muscles and cause ptosis and both can be worse as the day progresses for different reasons; both have an immune-mediated aetiology with myasthenia gravis well recognised as antibody-mediated and narcolepsy shown to have increased T-cell activity; both have documented association with other autoimmune disorders.
Conclusion This case highlights an unusual presentation of two very rare conditions with both overlapping clinical features. Co-occurrence is incredibly rare, but caution and consideration of other differential diagnoses is advised if symptoms do not respond to treatment, or are not fully consistent with typical narcolepsy. The possible co-existence of other immune-mediated disorders should be borne in mind, with a low threshold to involve other expert professionals.
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