Paraneoplastic Antibodies (Anti-Hu/Yo/Ri)

TL;DR

List: Paraneoplastic Antibodies (Anti-Hu/Yo/Ri) is a frequently tested neuroimmunology topic in MRCP Part 1, particularly in questions linking neurological syndromes with occult malignancy. The highest-yield approach is to memorise each antibody together with its characteristic neurological syndrome and associated tumour. This guide summarises the most examinable associations, common pitfalls, a short clinical scenario, and practical revision tips.

Why this matters

Paraneoplastic syndromes occur when an immune response against a tumour cross-reacts with normal neural tissue. Neurological symptoms often develop months before the underlying cancer is diagnosed, making these disorders important clinical clues.

Typical examination themes include:

• identifying the underlying malignancy

• matching antibodies to neurological syndromes

• recognising classical clinical presentations

• distinguishing paraneoplastic disorders from metastatic disease

• understanding which antibodies affect the central versus peripheral nervous system

Questions are often integrated with oncology or respiratory medicine, especially involving small-cell lung carcinoma (SCLC).

For a broader revision of neurological and oncological topics, see the MRCP Part 1 overview:https://www.crackmedicine.com/mrcp-part-1/

Core sections

What are paraneoplastic antibodies?

Paraneoplastic antibodies are autoantibodies produced in response to tumour antigens that resemble neuronal proteins.

Importantly:

• they serve primarily as diagnostic markers

• they indicate an immune-mediated process

• neurological damage is mainly T-cell mediated for many antibodies

• neurological symptoms frequently precede cancer diagnosis

Their presence should always prompt a search for an underlying malignancy.

The five most tested subtopics

1. Anti-Hu (ANNA-1)

This is the single highest-yield antibody for MRCP.

Associated tumour

• Small-cell lung carcinoma (most common)

Typical neurological syndromes

• Sensory neuronopathy

• Limbic encephalitis

• Encephalomyelitis

• Cerebellar degeneration

• Autonomic neuropathy

Exam pearl

An older smoker presenting with painful sensory neuropathy should immediately raise suspicion of small-cell lung cancer with Anti-Hu antibodies.

2. Anti-Yo (PCA-1)

Anti-Yo primarily affects the cerebellum.

Associated tumours

• Breast carcinoma

• Ovarian carcinoma

• Other gynaecological malignancies

Typical presentation

• Progressive cerebellar ataxia

• Dysarthria

• Gait instability

• Nystagmus

Symptoms often progress rapidly over weeks.

3. Anti-Ri (ANNA-2)

Anti-Ri is less common but highly characteristic.

Associated tumours

• Breast carcinoma

• Small-cell lung carcinoma

Characteristic neurological syndrome

• Opsoclonus-myoclonus syndrome

Patients may also develop:

• brainstem encephalitis

• ataxia

• cranial nerve abnormalities

Opsoclonus ("dancing eyes") is the key examination clue.

4. Limbic encephalitis

Several antibodies may cause limbic encephalitis.

Clinical features include:

• memory impairment

• personality change

• seizures

• confusion

• behavioural disturbance

Common associated antibodies:

• Anti-Hu

• Anti-Ma2

• Anti-amphiphysin

• Anti-CV2/CRMP5

The underlying malignancy should always be investigated.

5. Cerebellar degeneration

Rapid cerebellar deterioration strongly suggests a paraneoplastic syndrome.

Typical symptoms include:

• truncal ataxia

• dysarthria

• intention tremor

• nystagmus

• gait instability

Most commonly associated antibodies:

• Anti-Yo

• Anti-Hu

• Anti-Tr

• Anti-CV2

High-yield antibody summary

Antibody	Typical tumour	Classical syndrome
Anti-Hu (ANNA-1)	Small-cell lung carcinoma	Sensory neuropathy, limbic encephalitis
Anti-Yo (PCA-1)	Breast, ovarian cancer	Cerebellar degeneration
Anti-Ri (ANNA-2)	Breast cancer, SCLC	Opsoclonus-myoclonus
Anti-amphiphysin	Breast cancer, SCLC	Stiff-person syndrome
Anti-CV2 (CRMP5)	Small-cell lung carcinoma	Chorea, neuropathy
Anti-Ma2	Testicular germ-cell tumour	Limbic and brainstem encephalitis
Anti-Tr	Hodgkin lymphoma	Cerebellar degeneration
Anti-recoverin	Small-cell lung carcinoma	Cancer-associated retinopathy
Anti-SOX1	Small-cell lung carcinoma	Lambert-Eaton syndrome association
Anti-GABA-B receptor*	Small-cell lung carcinoma	Limbic encephalitis

*Surface antibody with therapeutic implications.

10 high-yield examination facts

1. Anti-Hu is most strongly associated with small-cell lung carcinoma.

2. Anti-Yo classically causes cerebellar degeneration.

3. Anti-Ri is associated with opsoclonus-myoclonus.

4. Neurological symptoms often appear before cancer diagnosis.

5. MRI may initially be normal.

6. CSF may show inflammatory changes.

7. Small-cell lung carcinoma is the commonest underlying tumour overall.

8. Anti-Hu commonly produces sensory neuronopathy.

9. Anti-Yo is strongly associated with breast and ovarian cancer.

10. Treatment focuses on both tumour therapy and immunotherapy.

Practical examples / mini-cases

Mini Case

A 66-year-old lifelong smoker develops progressive numbness affecting both upper limbs followed by severe gait instability. Neurological examination demonstrates loss of proprioception without significant weakness. CT imaging later identifies a hilar lung mass.

Which antibody is most likely to be positive?

A. Anti-Yo

B. Anti-Ri

C. Anti-Hu

D. Anti-Tr

E. Anti-Ma2

Answer: C. Anti-Hu

Explanation

Painful sensory neuronopathy occurring before the diagnosis of small-cell lung carcinoma is the classic presentation of Anti-Hu-associated paraneoplastic syndrome.

Practical study-tip checklist

✔ Memorise tumour–antibody pairs rather than isolated antibodies.

✔ Learn the "big three": Anti-Hu, Anti-Yo and Anti-Ri first.

✔ Associate Anti-Hu with smokers and small-cell lung carcinoma.

✔ Associate Anti-Yo with cerebellar degeneration in women with breast or ovarian cancer.

✔ Remember that opsoclonus almost always points towards Anti-Ri in MRCP-style questions.

✔ Revise neurological syndromes alongside underlying malignancies.

✔ Practise integrated oncology and neurology questions using the Free MRCP MCQs:https://www.crackmedicine.com/qbank/

✔ Consolidate concepts with structured MRCP video lectures:https://www.crackmedicine.com/lectures/

Common pitfalls

• Confusing Anti-Hu with Lambert-Eaton syndrome antibodies (P/Q-type voltage-gated calcium channel antibodies).

• Assuming all cerebellar degeneration is caused by Anti-Hu—Anti-Yo is the classic association.

• Forgetting that neurological symptoms frequently precede tumour diagnosis.

• Memorising antibodies without learning their characteristic neurological syndromes.

• Ignoring the strong association between small-cell lung carcinoma and multiple paraneoplastic antibodies.

FAQs

Which paraneoplastic antibody is most associated with small-cell lung carcinoma?

Anti-Hu is the classic answer in MRCP Part 1. Small-cell lung carcinoma is also associated with several other antibodies, but Anti-Hu remains the highest-yield association.

What neurological syndrome is classically linked to Anti-Yo?

Anti-Yo is strongly associated with subacute cerebellar degeneration, especially in women with breast or ovarian carcinoma.

Which antibody causes opsoclonus-myoclonus syndrome?

Anti-Ri is the classical antibody associated with opsoclonus-myoclonus syndrome and may occur with breast carcinoma or small-cell lung carcinoma.

Do neurological symptoms occur before cancer diagnosis?

Yes. In many patients, neurological symptoms develop months before the malignancy is detected, making recognition clinically important.

How should I revise paraneoplastic antibodies for MRCP Part 1?

Focus first on the classic antibody–tumour–syndrome combinations. Regular MCQ practice and spaced repetition improve long-term recall more effectively than memorising long antibody lists.

Ready to start

Paraneoplastic antibodies are best learnt through repeated clinical application rather than rote memorisation. Strengthen your understanding by studying integrated oncology and neurology topics in the MRCP Part 1 overview, practising clinically relevant questions in the Free MRCP MCQs, and reinforcing concepts with comprehensive MRCP video lectures.

Sources

1. MRCP(UK). https://www.mrcpuk.org/

2. Graus F, Vogrig A, Muñiz-Castrillo S, et al. Updated Diagnostic Criteria for Paraneoplastic Neurologic Syndromes. Neurology. 2021.

3. Dalmau J, Rosenfeld MR. Paraneoplastic Syndromes of the CNS. The Lancet Neurology.

4. UpToDate. Paraneoplastic neurologic syndromes.

5. European Academy of Neurology Guidelines on Paraneoplastic Neurological Syndromes.