POST POLIO SYNDROME

POST POLIO SYNDROME

Accepted criteria for diagnosis of postpolio syndrome (PPS) are a prior history of poliomyelitis, a stable period after recovery, a residual deficit of the initial polio, new muscle weakness, and sometimes, new muscle atrophy.

Fatigue and muscle pain need not be present to meet the criteria for the syndrome.

PATHOPHYSIOLOGY

One possible cause of postpolio syndrome (PPS) is decompensation of a chronic denervation and reinnervation process to the extent that the remaining healthy motor neurons can no longer maintain new sprouts; thus, denervation exceeds reinnervation.

A second possible mechanism for PPS is motor neuronal loss due to reactivation of a persistent latent virus. In addition to muscle atrophy and denervation, foci of perivascular and interstitial inflammatory cells have been found on 50% of biopsies of patients with PPS.

Activated T cells and immunoglobulin M and immunoglobulin G antibodies specific for gangliosides also have been found.

Another possibility is an infection of the polio survivor's motor neurons by an enterovirus that is different from the one responsible for the patient's polio.

Others sources hypothesize that PPS is merely the loss of strength due to the usual stresses of aging and weight gain. In patients with PPS, these processes occur in muscles that already are weak, so the consequences are more noticeable compared with those of patients who have not had polio.

FREQUENCY

The incidence of postpolio syndrome (PPS) in previous acute polio patients ranges from approximately 22-68%. PPS is estimated to occur in 28.5% of persons who had paralytic polio.

The current prevalence is approximately 1.6 million cases. Suggestions have been made that 100% of polio survivors, if tracked for a long period, can develop some symptoms of PPS.

AGE

The onset of postpolio syndrome is approximately 30 years after the acute polio.

CLINICAL

HISTORY

Symptoms of postpolio syndrome (PPS) usually appear earlier in patients who have very severe residual weakness, individuals who had early bulbar respiratory difficulty in the acute illness, and persons who were older when they contracted acute polio. PPS symptoms tend to occur first in the weaker muscles.

• Fatigue - In individuals without polio or PPS, the functional consequences of aging and loss of motor units may be unnoticeable until a very advanced age. In the individual with PPS, any further loss of strength may be more readily apparent. In contrast to patients with chronic fatigue syndrome, postpolio fatigue is prominent in the early hours of the afternoon and decreases after brief periods of rest. PPS-related fatigue usually does not prevent patients from working.

  • Central

    • Pathogenesis can include chronic pain, type A personality, depression, dysfunctional reticular-activated system, sleep disorders, and respiratory dysfunction.

    • PPS produces somnolence and difficulty in concentrating and remembering.

  • Peripheral

    • Pathogenesis may be metabolic exhaustion of the enlarged motor units, neuromuscular junction transmission defects, scarring within the motor neurons, or loss of motor units due to aging.

    • PPS produces decreased muscular endurance and increased muscular fatigability.

• Weakness

  • A number of functional etiologies for weakness have been hypothesized, including disuse, overuse, and chronic weakness, as well as weight gain.

  • Asymmetrical and scattered weakness may be present.

  • Some authors have found evidence that previously unaffected muscles later become weak; in these cases, they discovered that the patient was unaware or had not been told that the particular muscle had been affected during the acute episode.

• Muscle pain

  • Deep aching pain may be a component of a myofascial pain syndrome or fibromyalgia.

  • This feature is extremely prevalent in PPS. Using a retrospective, cross-sectional survey, Stoelb et al investigated the frequency and most common sites of pain in patients with postpolio syndrome.4 Pain symptoms were reported by 57 (90.5%) of the 63 study participants; pain was reported most often in the shoulders, legs, hips, and lower back, with the most intense pain occurring in the legs, knees, wrists, head, and lower back.

• Gait disturbance - Difficulty with gait is caused by progressive weakness, pain, osteoarthritis, or joint instability; it is common in patients who previously used assistive devices but later discarded them.

• Respiratory problems

  • Respiratory disorders are most prevalent in patients with residual respiratory muscle weakness.

  • These changes cause chronic microatelectasis, diminished pulmonary compliance, increased chest wall tightness, chronic alveolar hypoventilation, decreased cough and expiratory flow, and decreased clearing of secretions.

  • The new respiratory difficulties are not only related to new respiratory muscle weakness but also to scoliosis, pulmonary emphysema, cardiovascular insufficiency, or poor posture.

  • A central component also may occur because acute bulbar polio often affects the medullary structures, including the reticular formation and sleep regulatory system.

• Swallowing problems

  • These difficulties can occur in patients with bulbar and non-bulbar postpolio.

  • Subclinical asymmetrical weakness in the pharyngeal constrictor muscles is almost always present in all postpolio muscular atrophy patients, including those who do not complain of new swallowing difficulties.

• Autonomic dysfunction - The cause is unclear; the peripheral component could include muscular atrophy and, therefore, diminished heat production.

• Sleep apnea

  • This disorder is not uncommon in patients left with residual bulbar dysfunction or severe respiratory compromise.

• Sleep apnea appears to be due to a combination of the following:

  • Central apnea, due to a residual dysfunction of the surviving bulbar reticular neurons

  • Obstructive apnea, due to pharyngeal weakness and increased musculoskeletal deformities from scoliosis or emphysema

  • Postpolio muscular atrophy, resulting in diminished muscle strength of the respiratory, intercostal, and abdominal muscle groups

• Flat-back syndrome

  • Another possible symptom in some patients with PPS is the flat-back syndrome, which consists of the inability to stand erect because of forward flexion of the trunk and pain in the low back and legs.

  • The flat-back syndrome typically occurs in patients with diminished lumbar lordosis as a result of instrumentation of the spine for scoliosis, vertebral fracture, or degenerative joint disease.

  • The trunk extensor musculature plays an essential role in maintaining upright posture, and it may be that PPS-related weakness in this musculature represents a major contributing factor to the flat-back syndrome in these patients.

PHYSICAL

In persons with postpolio syndrome, progressive weakness and atrophy may be observed in muscles that were affected initially by the poliovirus or in muscles that were spared clinically, which tends to happen in an asymmetrical distribution.

Fasciculations sometimes can be observed in atrophic muscles, as a result of the lower motor neuron injury.

DIAGNOSIS

LABORATORY STUDIES

• Obtain the following laboratory studies to exclude conditions other than postpolio syndrome:

  • Complete blood cell (CBC) count

  • Cerebrospinal fluid

• Swallowing studies

IMAGING STUDIES

• Computed tomography (CT) scanning and magnetic resonance imaging (MRI) can be ordered to rule out other possible diagnoses or structural neurologic processes (eg, stroke, multiple sclerosis, tumor).

OTHER TESTS

Ø  Electrodiagnostic studies are used to rule out other neurologic or neuromuscular disorders in the differential diagnosis. The following 5 phases of electrodiagnostic study findings of anterior horn cell disease have been recognized:

o    Acute myelitis (first month)

o    Early recovery (2-12 mo)

o    Late recovery

o    Functional stability

o    Late changes during functional stability (eg, fasciculations, positive waves, fibrillations, increased amplitude and duration of motor unit potentials)

Ø  In postpolio syndrome (PPS), sensory conductions should be normal; motor conductions usually are normal but may be slow. In late stages, amplitude decreases significantly.

Ø  Single-fiber electromyography reveals increased jitter and blocking. This observation is related to the fact that in PPS, variable degrees and different types of neuromuscular transmission failure have been found in affected patients who had associated histologic signs of reinnervation in their muscle biopsies.

Ø  Functional and structural abnormalities of neuromuscular junctions are common, but not necessary, conditions for the diagnosis of PPS. These neuromuscular junction transmission defects typically are observed in the early stage of the neuronal degeneration that produces PPS. Whether neuromuscular junction transmission defects increase with the passage of time is unclear.

Histologic Findings

In the chronically denervated muscles of patients with postpolio syndrome, there are secondary myopathic features, including endomysial inflammation and rare vacuolated fibers.

TREATMENT

PHYSICAL THERAPY

The basic management principles for individuals with postpolio syndrome include energy conservation and pacing one's activities.

Although basic, these activity modifications may be difficult for some patients to accept.

Reports on exercises are conflicting, but the key factor seems to be exercise intensity. Strengthening exercises should be non-fatiguing.

A specific suggestion is to exercise every other day, and the perceived rate of exertion should be less than "very hard."

Loads should be held for only 4-5 seconds, and there should be a 10-second rest between bouts and a 5-minute rest between sets.

The patient should perform about 3 sets of 5-10 repetitions.

In addition to specifying exercises for those body areas experiencing the deleterious effects of disuse, the exercise prescription also should consider how to protect

(1) muscles and joints that are experiencing the adverse effects of overuse and

(2) body areas with very significant chronic weakness (generally, areas where the muscles have less than antigravity strength on manual muscle testing).

Results of these exercises vary. Strengthening programs performed as described show a 60% increase on isokinetic strength, improved cardiorespiratory status, no decline in strength in 6-12 months, and 5% increase in isometric strength.

Electrical stimulation has been used to strengthen weakened muscles or to reeducate muscles weakened through disuse, as well as to decrease pain.

For myofascial pain, consider heat, electrical stimulation; trigger point injections, stretching exercises, biofeedback, muscle relaxation exercises, or static magnetic fields for trigger points.

For gait disturbances, assistive devices can be used, but sometimes patients refuse because of the philosophy of "not giving in." Treatment also can involve limitation of ambulation to shorter distances and the use of orthotics for joint protection.

OCCUPATIONAL THERAPY

Patients with postpolio syndrome usually benefit from different adaptive techniques and equipment to perform any activities of daily living, as well as education and energy conservation techniques.

SPEECH THERAPY

Speech evaluation in persons with postpolio syndrome usually is recommended with any suggestion of swallowing problems. The therapist teaches the patient about different techniques to improve his/her swallowing function.

MEDICATION

Medications, most of which address fatigue, have been used with only partial success in patients with postpolio syndrome. Contradictory information is reported on the use of antivirals.

Some authors have found no significant improvement with antivirals as compared with placebo. Amantadine may act to release dopamine from dopaminergic terminals and other central sites. Corticosteroids have been studied, but with no good results.

ANTICHOLINESTERASES

Some authors have reported that one of the mechanisms for production of fatigue may be related to neuromuscular junction transmission deficits; however, treatment with anticholinesterases has been successful in only half of the cases; this low success rate has been attributed to the variety of neuromuscular junction defects believed to be present in postpolio syndrome.

PYRIDOSTIGMINE (MESTINON)

Acts in smooth muscle, the CNS, and secretory glands where it blocks action of acetylcholine at parasympathetic sites and facilitates transmission of impulses across the myoneural junction.

Adult: 60 mg PO tid (in experimentation) 

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Caution in bronchial asthma and those receiving a cardiac glycoside; overdose may cause cholinergic crisis, which may be fatal; atropine IV should be readily available for treatment of cholinergic reactions

IMMUNOGLOBULINS

Modulate activity of immune system.

IMMUNOGLOBULIN [(IV) (SANDOGLOBULIN)]

Intravenous immunoglobulin has been recently studied in the treatment of symptoms related to postpolio syndrome. Results show that it could be a supportive treatment option for subgroups of patients with postpolio syndrome.

Features that may be relevant to its efficacy include neutralization of circulating myelin antibodies through anti-idiotypic antibodies; down-regulation of proinflammatory cytokines, including IFN-gamma; blockade of Fc receptors on macrophages; suppression of inducer T and B cells and augmentation of suppressor T cells; blockade of the complement cascade; promotion of remyelination; 10% increase in CSF IgG.

Adult: 2 g/kg IV over 2-5 d 

Pregnancy

C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus

Precautions

Check serum IgA before IVIG (use an IgA-depleted product, eg, Gammagard S/D); infusions may increase serum viscosity and thromboembolic events; infusions may increase risk of migraine attacks, aseptic meningitis (10%), urticaria, pruritus, or petechiae (2-30 d postinfusion)

Increases risk of renal tubular necrosis in elderly patients and in patients with diabetes, volume depletion, and preexisting kidney disease; lab result changes associated with infusions include elevated antiviral or antibacterial antibody titers for 1 mo, 6-fold increase in ESR for 2-3 wk, and apparent hyponatremia

ANTICONVULSANT AGENTS

May reduce morbidity of the disease.

LAMOTRIGINE (LAMICTAL)

Some preliminary studies suggest the efficacy of lamotrigine in enhancing the quality of life and symptoms of patients with postpolio syndrome.

Inhibits release of glutamate and inhibits voltage-sensitive sodium channels, leading to stabilization of neuronal membrane.

Adult: Monotherapy: Initial: 50-100 mg/d PO bid

Maintenance: 100-400 mg/d PO qd or divided bid, not to exceed 500 mg/d

Adjunct therapy with valproic acid: Initial dose: 25 mg PO qod

Maintenance: 50-200 mg/d PO in 1-2 divided doses, not to exceed 200 mg/d.