Neuromuscular Manifestations of Neoplasms and Paraneoplastic Syndromes

Definition

The term “paraneoplastic syndromes” refers to symptoms resulting from damage to organs or tissues that are remote from the site of a malignant neoplasm or its metastases.¹Paraneoplastic neurological syndromes (PNS) are immune-mediated erroneous attacks on the central or peripheral nervous systems, or both, directed originally against the tumor itself.²

Etiology

An immunologic response is directed against shared antigens that are ectopically expressed by the tumor, but otherwise exclusively expressed by the nervous system. For unknown reasons, the immune system identifies these antigens as foreign and mounts an immune attack against them.³

Epidemiology including risk factors and primary prevention

PNS are rare diseases occurring in less than about 0.01% of patients with cancer.4 However, the incidence of paraneoplastic disorders vary with the neurologic syndrome and type of tumor. The more common syndromes are Lambert-Eaton myasthenic syndrome (LEMS), which affects approximately 3% of patients with small-cell lung cancer (SCLC), and myasthenia gravis (MG), which affects 15% of all patients with thymoma. However, it should be noted that not all cases of MG are considered to be paraneoplastic. One or more paraneoplastic neurologic disorder is present in up to 9% of patients with with SCLC.³

Patho-anatomy/physiology

Currently, it is thought that most or all paraneoplastic neurologic disorders are immune-mediated.¹ The mechanism entails ectopic expression by a tumor of an antigen that normally is expressed exclusively in the nervous system. The same antigen may be processed by the immune system differently, depending on whether it is expressed in a cancer cell versus a normal cell. This suggests that additional factors may be involved in the immune response to the antigen.^3,4

Disease progression including natural history, disease phases or stages, disease trajectory (clinical features and presentation over time)

Syndromes defined as ‘classical’ PNS include encephalomyelitis, limbic encephalitis, subacute cerebellar degeneration, sensory neuronopathy, opsoclonus-myoclonus, chronic gastrointestinal pseudo-obstruction, LEMS and dermatomyositis. Each syndrome has a unique clinical presentation that often precedes a diagnosis of cancer. They may be rapidly progressive, in many cases leaving the patients severely debilitated within weeks to months.⁴Most PNS associated with onconeural antibodies usually have a subacute, aggressive clinical course and then stabilize.⁵

Specific secondary or associated conditions and complications

MG is associated with thymoma. LEMS and paraneoplastic limbic encephalitis are associated with SCLC. Encephalitis resulting from antibodies against N-methyl-D-aspartate receptors occur in ovarian teratoma.⁶ Dermatomyositis has been reported in cases of breast cancer.⁷ Paraneoplastic cerebellar degeneration is associated with Hodgkin lymphoma, breast cancer, SCLC, ovarian cancer, and prostate carcinoma.⁶

History

PNS presentation often precedes cancer diagnosis. MG presents as asthenia, particularly extraocular muscle and ptosis. LEMS manifests as asthenia of the scapular and pelvic girdles, xerostomia, and sexual impotence. Paraneoplastic limbic encephalitis is characterized by depression, seizures, and memory loss. Paraneoplastic cerebellar degeneration causes diplopia, ataxia, and dysphagia.^6,8

Physical examination

A thorough physical examination should include reflexes, muscle strength, muscle tone, sense of touch, vision and hearing, coordination, balance, mental status, mood, palpation for pathological lymph nodes, rectal and pelvic examination, and palpation of breasts and testis.^9,8

Clinical functional assessment: mobility, self care cognition/behavior/affective state

Locations for functional assessment of muscle weakness include facial (‘horizontal smile’, inability to whistle), ocular (double vision, ptosis, disconjugate eye movements), bulbar (weak cry, dysphagia, cough during meals), neck (poor head control), trunk (difficulty sitting up), respiratory (use of accessory muscles), shoulder girdle, forearm/hand, pelvic girdle, and leg/foot.¹⁰

Laboratory studies

Antibodies can be detected in the serum or CSF. Testing of serum alone may suffice for “classical” paraneoplastic antibodies, but it is not sufficient for some autoimmune encephalitide associated with antibodies against cell surface or synaptic proteins. Low levels of paraneoplastic antibodies may be seen in patients without PNS.³

Imaging

MRI can assist in the diagnosis of limbic encephalitis because the medial temporal lobes, the site of major pathology, and often show increased signal on fluid-attenuated inversion recovery (FLAIR) images and occasionally areas of contrast enhancement. Patients with paraneoplastic cerebellar degeneration may develop signs of atrophy detectable by MRI several months after the onset of symptoms. PET scan of the brain using fluorodeoxyglucose (FDG-PET) will occasionally identify hypermetabolism of the medial temporal lobes in patients with limbic encephalopathy, or of the cerebellum in patients with paraneoplastic cerebellar degeneration.³

Supplemental assessment tools

PNS associated with electrophysiologic findings include LEMS, MG, and dermatomyositis.³For LEMS, electrodiagnostic studies demonstrate a compound muscle action potential (CMAP) that is often less than 10% of normal. However, when stimulated at frequencies from 22 to 50 Hz, the compound muscle action potential increases in size. An increase of 100% is typical of LEMS.¹¹ For MG, electrodiagnostic studies include repetitive nerve stimulation (RNS) studies and single-fiber electromyography (SFEMG). In RNS, the nerve is electrically stimulated at 2 to 3 Hertz, and shows a decremental response in the CMAP amplitude with the few stimuli.¹²

Early prediction of outcomes

Some reports suggest a more limited disease distribution and better outcome among patients with SCLC who develop immunity to paraneoplastic antigens. 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 PNS.³

Environmental

Among those who are diagnosed with LEMS who are later found to have cancer will likely have a history of long-term smoking.¹³ For MG, medications including aminoglycosides, macrolides, beta-blockers, ACE inhibitors, quinidine, lidocaine, procainamide, phenytoin, prednisone, interferon, and D-penicillamine, can cause exacerbation of symptoms.¹⁴

Social role and social support system

Patients who have cancer may find the physical, emotional, and social effects of the disease to be stressful. Effective coping strategies to deal with stress, such as relaxation and stress management techniques, have been shown to have lower levels of depression and anxiety.¹⁵

Professional issues (Identify and/or consider issues relevant to this topic in the areas of ethics, quality of life, professionalism and safety.)

As PNS are rare, the diagnosis is difficult and frequently the patient is misdiagnosed. Neurological symptoms usually develop before the diagnosis of the tumor.⁴ Prompt oncologic treatment is beneficial. The failure of the neurologic syndrome to respond to treatment may be due to irreversible neuronal damage that occurred before treatment.³

Available or current treatment guidelines

Two general approaches to treatment include: removal of the antigen source by treatment of the underlying tumors, and suppression of the immune response. Immunosuppression is beneficial for some conditions, such as the LEMS, MG, and encephalitides associated with antibodies against cell surface antigens. Plasma exchange or IVIG is effective in suppressing the immune response and improving neurologic status. Second line therapies include rituximab and cyclophosphamide. Syndromes that usually do not respond to treatment includes most of the classical paraneoplastic syndromes associated with antibodies against intracellular antigens.³ Some examples include limbic encephalitis, opsoclonus-myoclonus syndrome, and Lambert Eaton myasthenic syndrome.¹⁶

At different disease stages

Rapid detection and immediate treatment of the underlying tumor appears to offer the best chance of stabilizing the patient and preventing further neurological deterioration.⁹ The different subtypes of PNS are defined by the presence or the absence of paraneoplastic antibodies and the type of antibodies. Management and treatment should be tailored to each subtype.⁴ There are no established protocols for the treatment of most paraneoplastic syndromes, but if the patient’s condition is deteriorating, the physician usually uses a combination of either plasma exchange or intravenous immune globulin and immunosuppressive agents such as corticosteroids, cyclophosphamide, or tacrolimus. A few isolated case reports describe responses to various immunotherapeutic interventions encourage physicians to combine immunotherapy with treatment of the cancer in a desperate situation. Because the pathologic features of paraneoplastic neurologic disorders suggest that a destructive immune response is typically present, treatment with immunosuppression should begin as expeditiously as possible. Some disorders, such as the Lambert–Eaton myasthenic syndrome and myasthenia gravis, respond well to immunosuppression and subsequently to treatment of the underlying tumor.¹

Coordination of care (Recommend useful team approaches or models of care relevant to this topic.)

Coordination between the physiatrist, therapist, oncologist, and neurologist are necessarily. Particular attention should be paid when coordinating physical therapy and any concurrent cancer treatment to ensure there are no scheduling conflicts and to ensure that the patient can actively participate in therapy. In severely debilitated patients, for example, the elderly and bedridden, immunotherapy treatment is often withheld because of the very small chance of clinically relevant neurological improvement.⁹

Patient & family education

The patient should be aware of the cancer prognosis and what symptoms reflect worsening prognosis of the cancer and what symptoms are purely associated with nerve damage that resulted from the PNS. Furthermore, the patient and family should be aware of which subsets of PNS can be treated with immunotherapy.

Measurement of Treatment Outcomes including those that are impairment-based, activity participation-based and environmentally-based.

Improvement from immunotherapy treatment can be measured by any increase in Rankin score or a 10-point increase in Barthel functional index.¹⁷ Functional Independence Measure (FIM) is a useful measurement in the setting of acute inpatient rehabilitation.¹⁸

Translation into Practice: practice “pearls”/performance improvement in practice (PIPs)/changes in clinical practice behaviors and skills

Symptoms of PNS may include ataxia, dizziness, nystagmus, difficulty swallowing, loss of muscle tone, loss of fine motor coordination, vision problems, and sensory loss in the limbs. The PNS may precede the diagnosis of underlying malignancy. In such cases, the clinical syndrome and identification of certain paraneoplastic antibodies may suggest a specific underlying tumor and direct investigations.³ The detection of antibodies is now expanded to those against neuronal surface antigens and synaptic receptors. These antibodies are excellent predictors of a better response to immunotherapy. Less frequently, patients may develop a second PNS clinically different from the first.⁵

Cutting edge concepts and practice

Novel associations between clinical encephalitic syndromes, and serologic presence of neuronal surface antibodies with or without underlying cancer have been developed in recent years. The classic paraneoplastic encephalitis syndromes (e.g., limbic encephalitis with SCLC) occur more frequently in older adults, are more likely to herald an underlying neoplasm, are clinically typically uniphasic with variable stabilization, and are limited in their response to therapy. As opposed to the classic PND, these recently characterized autoimmune encephalitis syndromes are generally more common, occur in younger age groups, respond more frequently to therapy, and may show relapses.¹⁹

Controversies and gaps in the evidence-based knowledge

No studies have conclusively proved that paraneoplastic antibodies are pathogenic; nevertheless, the paraneoplastic antibodies are useful diagnostic markers that can be used also to classify the different subtypes of PNS. The hypothesis that PNS are immune-mediated remains to be proved.⁴ Also, studies in animals have failed to reproduce PNS.¹

References

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