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Six weeks of worsening ataxia in a woman with lung cancer

Subacute cerebellar syndrome, opsoclonus, normal hearing — and a recent cancer diagnosis that reframes the differential.

The case

A 71-year-old retired teacher was diagnosed eight weeks ago with small-cell lung cancer (stage IIIb) and has just completed her first cycle of chemotherapy. She is referred to the ENT/balance clinic by her oncologist with a six-week history of progressive imbalance, slurred speech, and unsteadiness that has not responded to anti-emetics or rehabilitation. Her family report that she went from independent walking to needing a frame within four weeks, and she is no longer able to sit unsupported in a chair without leaning sideways.

On examination, gait is wide-based and ataxic; she cannot tandem-walk and has truncal instability when seated unsupported. Speech is scanning and irregular in volume. Limb examination shows bilateral dysmetria on finger-to-nose testing and dysdiadochokinesia. Eye movements show square-wave jerks at rest and intermittent brief bursts of multidirectional saccadic intrusions consistent with opsoclonus. There is no nystagmus on primary gaze, but gaze-evoked nystagmus appears on lateral gaze in both directions.

The head impulse test is normal bilaterally. Whispered-voice hearing is preserved at 60 cm in both ears. Audiometry is symmetric and within normal limits for age. There is no neck pain, no recent head trauma, and no relevant drug history beyond the chemotherapy regimen (etoposide and carboplatin, both completed at standard doses).

MRI of the brain shows mild diffuse cerebellar atrophy with no acute infarction, mass, or enhancement. Routine bloods are normal apart from a chronic mild anaemia attributable to her malignancy.

Question

What is the most likely diagnosis, and which investigation will confirm it?

Teaching point

Paraneoplastic cerebellar degeneration is the cerebellar syndrome that demands recognition. Its tempo (subacute, weeks rather than years), its multimodal signs (ataxia, opsoclonus, dysarthria, sometimes brainstem features), and its almost-pathognomonic association with specific cancers (small-cell lung → anti-Hu; ovary/breast → anti-Yo; Hodgkin → anti-Tr; breast/lung → anti-Ri) make the diagnosis tractable when considered. The neurological syndrome frequently precedes the cancer diagnosis by weeks to months, so a paraneoplastic workup is appropriate in any subacute cerebellar syndrome of unknown cause regardless of cancer status. The 2021 PNS-Care criteria (Graus et al.) standardise the diagnostic framework: high-risk antibody + classical syndrome + tumour confirmed within two years. Treatment is aimed at the underlying cancer plus immunotherapy (IVIG, plasmapheresis, rituximab, cyclophosphamide); the neurological prognosis depends heavily on speed of diagnosis and treatment, with anti-Yo carrying the worst outcome and anti-Tr the best. Cerebellar rehabilitation has a role for residual deficit.

References

  1. [1]Dalmau J, Rosenfeld MR. Paraneoplastic syndromes of the CNS. Lancet Neurology 2008;7(4):327–340. doi:10.1016/S1474-4422(08)70060-7
  2. [2]Graus F, Vogrig A, Muñiz-Castrillo S, et al.. Updated diagnostic criteria for paraneoplastic neurologic syndromes. Neurology Neuroimmunology & Neuroinflammation 2021;8(4):e1014. doi:10.1212/NXI.0000000000001014
  3. [3]Honnorat J, Antoine JC. Paraneoplastic neurological syndromes. Orphanet Journal of Rare Diseases 2007;2:22. doi:10.1186/1750-1172-2-22
  4. [4]Manto M, Marmolino D. Cerebellar ataxias. Current Opinion in Neurology 2009;22(4):419–429. doi:10.1097/WCO.0b013e32832b9897
Related moduleCerebellar Disorders →