Isolated diplopia associated with calcineurin inhibitor therapy in a patient with idiopathic membranous nephropathy: a case report

BACKGROUND: Neurotoxicity is a common side effect of treatment with calcineurin inhibitors. Tremors are frequently reported as the most common manifestation. Variable presentations can include headaches, seizures, visual hallucinations or blindness. Sixth nerve palsy has been reported in previous cases of bone marrow and cardiac transplant patients receiving calcineurin inhibitors. In many of these previously reported cases, the drug was administered intravenously and very high drug levels were found. CASE PRESENTATION: We report the first case of isolated diplopia in a patient being treated for idiopathic membranous glomerulonephritis. This is also the first report where the neurotoxicity induced by initial tacrolimus therapy persisted with subsequent cyclosporine therapy, two structurally different calcineurin inhibitors which share a common mechanism of action. In our case toxicity occurred after 3 months of therapy despite low serum concentrations and the symptoms resolved completely after discontinuation of the drugs. CONCLUSION: Our case provides further evidence that the neurotoxicity is a result of calcineurin inhibition. Monitoring of serum concentrations of these drugs has not been correlated with toxicity. The mean duration to onset of symptoms can be as much as 70 days suggesting accumulation of the drug in the central nervous system plays a role. Recognition of this condition is important for prompt diagnosis and appropriate management.