Paraneoplastic Cerebellar Degeneration

Paraneoplastic Cerebellar Degeneration

Overview

Paraneoplastic syndromes are a group of rare disorders that are triggered by an abnormal immune system response to an underlying malignant tumor. Patients with paraneoplastic neurological syndrome (PNS) most often present with neurologic symptoms before an underlying tumor is detected or coincide with the cancer diagnosis. 

Paraneoplastic neurologic syndromes include a variety of neurologic disorders, such as paraneoplastic cerebellar degeneration (PCD), that are caused by an immune-mediated mechanism rather than a metastatic complication or medication effect. Any malignancy can cause a paraneoplastic syndrome and any part of the nervous system can be involved depending on the type of primary malignancy. These syndromes affect 1–3% of all cancer patients. These syndromes are difficult to diagnose and typically respond poorly to treatment. However, the oncologic outcome of patients with antibody-associated paraneoplastic syndromes does not significantly differ from that of patients who do not have the antibodies or a paraneoplastic syndrome.

PCD is a rare nonmetastatic complication of a carcinoma, typically mediated by antibodies generated against tumor antigens (proteins). Similar proteins are also expressed on Purkinje cells and possibly other cells within the cerebellum. The cancer-fighting antibodies mistakenly attack these normal protein cells in the cerebellum. This immune activation in the central nervous system (CNS) results in cerebellar injury and dysfunction. 

An association between PCD and occult gynecologic cancers (breast or ovarian) was first identified in 1938, and the syndrome was described fully by Brain in 1951. Posner found that patients with PCD can be classified according to the presence or absence of an antibody that reacted with an antigen present in both the tumors and in cerebellar Purkinje neurons obtained from these patients.

Symptoms 

Ataxia: Uncoordinated muscle movements, leading to an unsteady, wide-based, lurching walk and difficulty with fine hand movements.

Nystagmus: Involuntary, rapid, small movements of the eyes.

Dysarthria: Slurred or slow, unsteady speech.

Dysphagia: Difficulty swallowing.

Dizziness and Vertigo: A sensation of spinning or unsteadiness.

Other Potential Symptoms

Cognitive and Mood Changes: Some patients may develop problems with executive function, spatial cognition, or memory, and some rare cases can include personality changes or disinhibition. 

Diplopia: Double vision. 

Malaise and Nausea: Some patients may have a preceding flu-like illness with low-grade fever, nausea, and vomiting. 

Progression and Characteristics

Subacute Onset: Symptoms tend to develop over weeks to months. 

Progressive Nature: The symptoms get worse over time. 

Plateauing: Symptoms often stabilize after about 6 months. 

Irreversible Damage: While treatment can help, the neurological damage is often permanent, leading to severe disability. 

Precedes Cancer Diagnosis: The onset of PCD symptoms can happen months or even years before a cancer diagnosis

Causes

Immune Response:

The presence of cancer triggers an immune response that produces autoantibodies. 

Cross-Reactivity:

These autoantibodies, which are also found in the tumor, mistakenly target and attack Purkinje cells in the cerebellum. 

Purkinje Cell Damage:

This immune attack results in the severe loss and destruction of Purkinje cells, leading to the neurological symptoms of PCD. 

Diagnosis

1. Clinical Evaluation

Neurological Symptoms:

The diagnosis is based on the acute or subacute onset of severe cerebellar dysfunction, including ataxia, dizziness, gait unsteadiness, dysarthria, and nystagmus. 

Exclusion of Other Causes:

Initial neuroimaging with MRI and CT scans is crucial to exclude other neurological conditions like strokes or primary brain tumors. 

2. Laboratory Tests 

Paraneoplastic Antibody Panel: This is the cornerstone of diagnosis.

Serum and CSF Tests: Blood and cerebrospinal fluid are tested for specific antibodies, such as anti-Yo (associated with breast and ovarian cancers) or anti-Hu (linked to small cell lung cancer).

Onconeural Antibodies: The detection of these antibodies helps direct the search for a specific type of underlying malignancy.

3. Cancer Screening

Comprehensive Search:

Because PCD often precedes the cancer diagnosis, a thorough search for the underlying malignancy is necessary. 

Imaging:

Fluorodeoxyglucose-positron emission tomography (FDG-PET) scans and other advanced imaging techniques can help detect hidden malignancies. 

Repeat Screening:

If no cancer is found initially, repeat cancer screenings are recommended every few months over a two-year period if high-risk antibodies are detected. 

4. Definitive Diagnosis 

A definite PCD diagnosis is made with the presence of a high-risk onconeural antibody, a neurological syndrome consistent with PCD, and a tumor that expresses the relevant antigen.

5. Importance of Early Diagnosis 

Early recognition and treatment of the underlying tumor are crucial for potentially stabilizing or improving the neurological condition in PCD.

Treatment

1. Treat the Underlying Cancer

Early identification is key:

Since PCD symptoms can precede the cancer diagnosis, finding and treating the underlying tumor is essential for improving outcomes. 

Cancer treatments:

This can involve a combination of chemotherapy, radiation therapy, or surgery to remove the tumor, depending on the type and stage of cancer. 

2. Immunotherapy

Goal: To reduce the immune system's attack on the cerebellar cells. 

Common therapies:

Corticosteroids: Such as prednisolone or methylprednisolone. 

Intravenous Immunoglobulins (IVIg): A preparation of antibodies from donated plasma. 

Plasma Exchange (Plasmapheresis): A process that removes harmful antibodies and proteins from the blood. 

Rituximab: A monoclonal antibody that targets B cells, another component of the immune system. 

Cyclophosphamide: A powerful immunosuppressant used as a second-line therapy. 

Other immunosuppressants: Such as tacrolimus or cyclosporine may be considered if initial treatments are not successful. 

3. Supportive Care 

Rehabilitation: A multidisciplinary approach that may include aggressive rehabilitation to help manage the neurological symptoms

Type of Doctor Department : A neurologist