Abstract We present an unusual movement disorder due to immune checkpoint inhibitors which responded rapidly to prednisolone.

Background Immune checkpoint inhibitors (ICIs) have revolutionised the scope of cancer therapy but can induce autoimmune effects on healthy organs, termed immune-related adverse events (irAEs). Their pathophysiology relies on the same mechanisms that confer anti-tumour activity and can affect any organ in the body. Neurological irAEs (n-irAEs) although rare, are potentially fatal. Differentiating n-irAEs from paraneoplastic syndromes and other neurological disorders can be challenging.

Case We present a case of n-irAE in a patient with metastatic renal cell carcinoma treated with two cycles of ipilimumab/nivolumab. Following the second cycle, the patient developed subacute onset of postural and rest tremor, predominantly affecting her upper limbs, head and tongue, of variable amplitude, with bradykinesia of foot tapping. Her gait was broad-based. MRI brain was unremarkable. CSF was lymphocytic (WBC 103 cells, 90% lymphocytes) with elevated protein (1.30g/L), normal CSF:serum glucose ratio, negative CSF culture and viral PCR. She was treated for ICI-associated neurotoxicity and responded rapidly to high-dose steroids.

Conclusion Physicians should be aware of the diverse presentations of n-irAEs, including unusual movement disorders. Close collaboration between neurologists and oncologists is imperative in the management of these patients.