Shrinking lung syndrome mimicking diaphragmatic palsy in systemic lupus erythematosus.

A 25-year-old woman presented with 1 year of progressive orthopnoea, initially explained as bilateral diaphragmatic paresis caused by seronegative myasthenia gravis. She required assisted ventilation and received pyridostigmine and corticosteroids. She had minimal (particularly proximal) symmetrical tetraparesis with apparent bilateral diaphragmatic weakness, but had normal sensation. Further investigation suggested an overlap myositis with shrinking lung syndrome from systemic lupus erythematosus. She improved following immunosuppression with pulse corticosteroids and rituximab, and at 3 months no longer needed bilevel positive airway pressure support.