Abstract
Case A 73-year-old oriental female was admitted with 4 years of fluctuating dysarthria and dysphagia. She had breast cancer in remission and stable IgG4 disease with prior intermittent low dose prednisolone and rituximab therapy.
Following COVID-19 infection, she developed progressive dysphagia with weight loss of 13kg, limb weakness and blurred vision.
On initial neurological exam, she was poorly muscled, without fasciculations. She had bifacial weakness, complex ophthalmoplegia, lingual and palatal weakness associated with dysarthria/dysphonia and neck flexor weakness. Deep tendon reflexes were brisk with normal tone and preserved limb strength without fatiguability.
Investigations and Management MRI brain and spine showed no leptomeningeal disease, infiltrative or compressive myelopathy.
IgG4 was chronically elevated at 3.67, with negative ANA, ENA and myositis antibodies.
EMG/NCS showed decrement on repetitive stimulation of right facial and spinal accessory nerves. Needle exam showed myopathic units in the masseter and genioglossus.
Anti-Acetylcholine antibody was negative. Anti-muscle specific kinase (MuSK) antibody was positive.
A diagnosis of myasthenia gravis (MG) was made. The patient had ongoing improvement in symptoms with weaning dose of prednisolone, and rituximab. At three months follow-up, she had normal speech, 4kg weight gain, and improvement in diplopia.
Conclusions Antibodies to MuSK antibodies are IgG4 subtype. MuSK MG is considered to be a form of IgG4 autoimmune disease, distinct from IgG4-related disease (IgG4-RD). There has only been one previous case report describing IgG4-related disease developing in a patient with known MuSK MG. We report the first case of diagnosis of IgG4-AID in a patient with established IgG4-RD.
