Paraneoplastic syndrome involves multi-organ system in the body with heterogeneous and complex clinical manifestations in the setting of underlying malignancy.

Clinical presentations are categorized based on the organ system as follows.

Nervous System

Signs and symptoms are based on the part of the nervous system that is affected by a paraneoplastic syndrome, for example, central nervous system, neuromuscular junction, or peripheral nervous system. A patient may present with seizure, cognitive dysfunction, personality change, psychosis, insomnia, ataxia, dysarthria, dysphagia, cranial nerve deficits, and sensorimotor abnormalities.

Central Nervous System

Paraneoplastic encephalitis/encephalomyelitis

Diverse and complex symptoms arising from cerebellar encephalitis, brainstem encephalitis, limbic encephalitis, and myelitis. Characterized by cognitive dysfunction, depression, personality changes, hallucinations, seizures, somnolence, autonomic dysfunction, and less commonly endocrine dysfunction if the hypothalamus is involved.[7]

Subacute cerebellar degeneration

It is commonly associated with breast cancer, small cell lung cancer, Hodgkin lymphoma, and ovarian cancer. Clinically manifested as ataxia, dysarthria, dysphagia, diplopia, dizziness, nausea, and vomiting.

Opsoclonus-myoclonus syndrome

Clinically characterized by uncontrolled rapid eye movement, body jerks, ataxia, hypotonia, irritability and commonly affects children less than 4 years. Opsoclonus is the common manifestation in children whereas ataxia is more prominent in adults.

Neuromuscular Junction

Myasthenia Gravis

Most commonly seen in patients with thymoma and is clinically manifested as a weakness of voluntary muscles and diaphragmatic weakness. Anti-AchR (acetylcholine receptor) antibody is positive in those patients, and electromyography (EMG) shows a decremental response to repetitive nerve stimulation.[8]

Lambert-Eaton myasthenic syndrome (LEMS)

It is caused due to impairment of voltage-gated calcium channels (VGCC) due to autoantibodies on the presynaptic membrane at neuromuscular junction which leads to decreased acetylcholine release. [8] LEMS is strongly associated with small cell lung cancer (SCLC), about 3% of patients develop LEMS, and it can occur at any stage of the disease. Clinically LEMS is characterized by weakness of the proximal muscles predominantly affecting thigh and pelvic muscles; patient generally have difficulty in strenuous activity; moreover, patients also have difficulties in basic activities such as climbing stairs, walking, and getting up from a chair. Symptoms are gradual in onset with slow progression. Patients also demonstrate autonomic symptoms such as dry mouth, decreased sweating, and constipation. Clinical examination is positive for diminished tendon reflexes.  The blood anti-VGCC antibodies are positive in approximately 85% of patients with LEMS.

Peripheral Nervous System

Autonomic neuropathy

Frequently associated with SCLC and thymoma. Autonomic neuropathy affects parasympathetic, sympathetic, and enteric nervous systems. Characterized by dry mouth, eyes, altered pupillary reflexes, bladder and bowel dysfunction, orthostatic hypotension. A patient may also manifest as chronic gastrointestinal (GI) pseudo-obstruction leading to constipation, nausea, vomiting, dysphagia, and abdominal distension.

Subacute sensory neuropathy

Characterized by paresthesia, pain, decreased sensation and deep tendon reflexes. It affects both upper and the lower extremities; distribution can be either multifocal, asymmetric or symmetric.

Endocrine

Cushing syndrome

Manifested as muscle weakness, weight gain, peripheral edema, centripetal fat distribution, and high blood pressure.[9] Blood workup significant for hypokalemia elevated cortisol level and elevated ectopic adrenocorticotropic hormone (ACTH) due to tumor cells.

Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

SIADH is more frequently seen in SCLC patients due to ectopic anti-diuretic hormone (ADH) by tumor cells.[10] Clinical manifestations vary from mild symptoms such as nausea, anorexia, fatigue, and lethargy to severe symptoms like confusion, seizures, respiratory depression, and coma. Laboratory findings are positive for hyponatremia, hyperosmolality and increased urine osmolality.

Hypercalcemia

It is frequently associated with lung cancer, multiple myeloma, and renal cell carcinoma. Hypercalcemia is mediated by different mechanisms such as the ectopic production of the parathyroid hormone-related peptide (PTHrP) by tumor cells, local osteolytic hypercalcemia and increased excess extrarenal vitamin D. Patients manifest as generalized weakness, lethargy, nausea, vomiting, altered mental status, bradycardia, acute renal failure, hypertonia, and hypertension.

Rheumatological

Paraneoplastic polyarthritis

Commonly involves large joints and is characterized by migratory, non-erosive, asymmetric polyarthritis.

Polymyalgia rheumatica

Manifested as pain and stiffness in the shoulder girdle, neck, and hip girdle.[11] It is most commonly associated with myelodysplastic syndrome.

Multicentric reticulohistiocytosis

Clinically characterized by papules, nodules, and destructive polyarthritis.

Hypertrophic osteoarthropathy

Clinically manifested as digital clubbing, joint swelling, and pain.

Hematological

Hematologic manifestations of the paraneoplastic syndrome are generally asymptomatic but can be manifested as pallor, fatigue, dyspnea, and venous thromboembolism. Hematologic syndromes are characterized by thrombocytosis, granulocytosis, eosinophilia, pure red cell aplasia, disseminated intravascular coagulation, and leukemoid reactions.

Dermatological

Acanthosis nigricans

Manifested as thickened hyperpigmented skin, usually in the axilla and neck region. Gastric adenocarcinoma is most commonly associated with acanthosis nigricans.[12]

Paraneoplastic pemphigus

Characterized by blistering and erosion of trunk, palms, and soles; also involves mucous membrane causing pain due to mucosal erosion. Commonly seen in patients with B-cell lymphoproliferative disorder.[13]

Sweet syndrome

This is also known as acute febrile neutrophilic dermatosis. It manifests as acute onset of painful, erythematous plaques, papules, and nodules accompanied by fever and neutrophilia.

Leukocytoclastic vasculitis

Typically manifests as palpable purpura on the lower extremities, but a patient may also experience cyanosis, pruritus, pain, and ulceration of the affected skin.

Dermatomyositis

Characterized by a heliotrope rash on the upper eyelids, Gottron papules on phalangeal joints, and an erythematous rash on the face, neck back, chest, and shoulders.[12] Also involves muscles as inflammatory myopathy and is manifested as proximal muscle weakness and muscle tenderness.

Renal

Electrolyte imbalance (hypokalemia, hypo or hypernatremia, hyperphosphatemia) causing nephropathy and acid-base disturbance due to ectopic hormones produced by tumor cells such as ACTH and ADH.[14] Nephrotic syndrome can also be one of the manifestations of paraneoplastic syndrome.

Miscellaneous

Fever, cachexia, anorexia, dysgeusia

Diagnosis of the suspected paraneoplastic syndromes is based on the exclusion of other etiologies as there are heterogeneous clinical manifestations.

An international panel of neurologists developed criteria for paraneoplastic syndrome affecting the nervous system into definite and possible categories [15][16].

Definite paraneoplastic syndromes

A classical neurological syndrome and malignancy which develops within 5 years of neurological disorder. Classical syndromes are encephalomyelitis, limbic encephalitis, subacute cerebellar degeneration, opsoclonus-myoclonus syndrome, Lambert Eaton myasthenic syndrome, subacute sensory neuropathy, chronic gastrointestinal pseudoobstruction, and dermatomyositis.

1. A nonclassical syndrome that improves significantly with the treatment of underlying malignancy and syndrome is not prone to spontaneous remission.
2. A nonclassical syndrome with the detection of paraneoplastic antibodies and malignancy that develops within 5 years of diagnosis of the neurological syndrome.
3. A classical or nonclassical neurological syndrome with well-recognized paraneoplastic antibodies. The well-recognized antibodies include anti-Hu, Yo, Ri, CV2/CRMP-5, Ma2, and amphiphysin.

Possible paraneoplastic syndrome

1. A classical syndrome without paraneoplastic antibodies and cancer but at high risk for an underlying malignancy.
2. A classical or nonclassical neurologic syndrome with partially characterized antibody but no cancer.
3. A nonclassical syndrome without paraneoplastic antibodies but with cancer within 2 years of a neurological syndrome.

A patient should be evaluated with a complete panel of laboratory, imaging, electrodiagnostic studies and biopsy of specific tissues if required.

• Complete blood count with differential
• Comprehensive metabolic panel
• Urinalysis
• Tumor markers
• Ectopic hormones level like PTHrP, ACTH, ADH
• Cerebrospinal fluid analysis (CSF)
• Protein electrophoresis o serum and CSF
• Assay of paraneoplastic antibodies in blood and CSF
• Skin biopsy
• Muscle biopsy

Management of the patients is based on type, severity, and location of the paraneoplastic syndrome. First, therapeutic options are to treat underlying malignancy with chemotherapy, radiation, or surgery. 

Other therapeutic options are immunosuppression with corticosteroids or other immunosuppressive drugs, intravenous immunoglobulins, plasma exchange, or plasmapheresis.

• Encephalopathy
• Encephalitis
• Personality disorder
• Dementia
• Myelitis
• Anemia
• Myelodysplastic syndrome
• Bone marrow failure
• Polycythemia Vera
• Chronic fatigue syndrome
• Mixed connective tissue disorder
• Dermatomyositis
• Scleroderma
• Systemic lupus erythematosus
• Polymyalgia rheumatica
• Acute glomerulonephritis
• Nephrotic syndrome

The diagnosis and management of paraneoplastic syndromes is difficult. In most cases, there is an underlying malignancy responsible. Because of the numerous causes, the condition is best managed by an interprofessional team that includes a pathologist, oncologist, radiologist, hematologist, nurse specialist, and an internist. Once the cause is discovered, it needs to be treated.

The management of the patients is based on type, severity, and location of the paraneoplastic syndrome. First, therapeutic options are to treat underlying malignancy with chemotherapy, radiation, or surgery. 

Other therapeutic options are immunosuppression with corticosteroids or other immunosuppressive drugs, intravenous immunoglobulins, plasma exchange, or plasmapheresis.