Objective We report a case of a 67-year-old man who presents with myasthenia gravis manifesting as an unusual pattern of weakness and positive IgG anti GM1 antibody.
Case The patient presented initially with 10 days history of ataxia, horizontal binocular diplopia on right gaze (right abducens palsy) and bilateral foot drop. Initial nerve conduction studies (NCS) were normal with no features of demyelination. CSF protein, sugar, cell type and count along with MRI brain and spine with contrast were unremarkable. The patient was treated as potential Guillian Barre syndrome variant. GQ1b antibody was negative but IgG anti GM1 antibodies were positive. Initial testing of AChR antibody level was equivocal. He was treated with 5 days of IVIG with symptomatic improvement. Six weeks later he represented with worsening fatigue and motor weakness including distal upper limb weakness. A repeat NCS showed mild slowing of sensory nerve conduction velocities. Repetitive nerve stimulation study revealed a decremental response of more than 30% area and 25% amplitude in both abductor digiti minimi muscles suggesting a post-synaptic NMJ disorder that is, myasthenia gravis. In the meantime, the patient developed new fatigable left eye ptosis (ice-test positive). Repeat AChR antibody testing was positive.
Conclusions This case highlights the varied clinical presentation of NMJ disorder like myasthenia gravis. Whether the positive anti GM1 antibody in this case is a pathological antibody or if its presence is coincidental or an epiphenomenon is unclear. NMJ junction is rich in gangliosides and potential NMJ dysfunction may occur but clinical cases of myasthenia associated with antiGM1 antibodies has not been reported to our knowledge.