Pathophysiology of a central cause of post-polio fatigue

Post-polio Syndrome: More Than Just a Lower Motor Neuron Disease

Post-polio syndrome (PPS) is a neurological condition that affects polio survivors decades after their initial infection. Despite its high prevalence, the etiology of PPS remains elusive, mechanisms of progression are poorly understood, and the condition is notoriously under-researched. While motor dysfunction is a hallmark feature of the condition, generalized fatigue, sleep disturbance, decreased endurance, neuropsychological deficits, sensory symptoms, and chronic pain are also often reported and have considerable quality of life implications in PPS. The non-motor aspects of PPS are particularly challenging to evaluate, quantify, and treat. Generalized fatigue is one of the most distressing symptoms of PPS and is likely to be multifactorial due to weight-gain, respiratory compromise, poor sleep, and polypharmacy. No validated diagnostic, monitoring, or prognostic markers have been developed in PPS to date and the mainstay of therapy centers on symptomatic relief and individualized rehabilitation strategies such as energy conservation and muscle strengthening exercise regimes. Despite a number of large clinical trials in PPS, no effective disease-modifying pharmacological treatments are currently available.

Compensatory effort parallels midbrain deactivation during mental fatigue: an fMRI study

Fatigue reflects the functioning of our physiological negative feedback system, which prevents us from overworking. When fatigued, however, we often try to suppress this system in an effort to compensate for the resulting deterioration in performance. Previous studies have suggested that the effect of fatigue on neurovascular demand may be influenced by this compensatory effort. The primary goal of the present study was to isolate the effect of compensatory effort on neurovascular demand. Healthy male volunteers participated in a series of visual and auditory divided attention tasks that steadily increased fatigue levels for 2 hours. Functional magnetic resonance imaging scans were performed during the first and last quarter of the study (Pre and Post sessions, respectively). Tasks with low and high attentional load (Low and High conditions, respectively) were administrated in alternating blocks. We assumed that compensatory effort would be greater under the High-attentional-load condition compared with the Low-load condition. The difference was assessed during the two sessions. The effect of compensatory effort on neurovascular demand was evaluated by examining the interaction between load (High vs. Low) and time (Pre vs. Post). Significant fatigue-induced deactivation (i.e., Pre>Post) was observed in the frontal, temporal, occipital, and parietal cortices, in the cerebellum, and in the midbrain in both the High and Low conditions. The interaction was significantly greater in the High than in the Low condition in the midbrain. Neither significant fatigue-induced activation (i.e., Pre<Post), nor its interaction with factor Load, was identified. The observed midbrain deactivation ([PreH - PostH]>[PreE- PostE]) may reflect suppression of the negative feedback system that normally triggers recuperative rest to maintain homeostasis.

A brain MRI study of chronic fatigue syndrome: evidence of brainstem dysfunction and altered homeostasis

To explore brain involvement in chronic fatigue syndrome (CFS), the statistical parametric mapping of brain MR images has been extended to voxel-based regressions against clinical scores. Using SPM5 we performed voxel-based morphometry (VBM) and analysed T(1) - and T(2) -weighted spin-echo MR signal levels in 25 CFS subjects and 25 normal controls (NC). Clinical scores included CFS fatigue duration, a score based on the 10 most common CFS symptoms, the Bell score, the hospital anxiety and depression scale (HADS) anxiety and depression, and hemodynamic parameters from 24-h blood pressure monitoring. We also performed group × hemodynamic score interaction regressions to detect locations where MR regressions were opposite for CFS and NC, thereby indicating abnormality in the CFS group. In the midbrain, white matter volume was observed to decrease with increasing fatigue duration. For T(1) -weighted MR and white matter volume, group × hemodynamic score interactions were detected in the brainstem [strongest in midbrain grey matter (GM)], deep prefrontal white matter (WM), the caudal basal pons and hypothalamus. A strong correlation in CFS between brainstem GM volume and pulse pressure suggested impaired cerebrovascular autoregulation. It can be argued that at least some of these changes could arise from astrocyte dysfunction. These results are consistent with an insult to the midbrain at fatigue onset that affects multiple feedback control loops to suppress cerebral motor and cognitive activity and disrupt local CNS homeostasis, including resetting of some elements of the autonomic nervous system (ANS).

Status epilepticus affects the gigantocellular network of the pontine reticular formation

BACKGROUND

The impairment of the pontine reticular formation (PRF) has recently been revealed to be histopathologically connected with focal-cortical seizure induced generalized convulsive status epilepticus. To elucidate whether the impairment of the PRF is a general phenomenon during status epilepticus, the focal-cortical 4-aminopyridine (4-AP) application was compared with other epilepsy models. The presence of "dark" neurons in the PRF was investigated by the sensitive silver method of Gallyas in rats sacrificed at 3 h after focal 4-AP crystal or systemic 4-AP, pilocarpine, or kainic acid application. The behavioral signs of the developing epileptic seizures were scored in all rats. The EEG activity was recorded in eight rats.

RESULTS

Regardless of the initiating drug or method of administration, "dark" neurons were consistently found in the PRF of animals entered the later phases of status epilepticus. EEG recordings demonstrated the presence of slow oscillations (1.5-2.5 Hz) simultaneously with the appearance of giant "dark" neurons in the PRF.

CONCLUSION

We argue that the observed slow oscillation corresponds to the late periodic epileptiform discharge phase of status epilepticus, and that the PRF may be involved in the progression of status epilepticus.

Fatigue in post-poliomyelitis syndrome: association with disease-related, behavioral, and psychosocial factors

OBJECTIVE

To determine the biopsychosocial correlates of general, physical, and mental fatigue in patients with postpoliomyelitis syndrome (PPS) by assessing the additional contribution of potentially modifiable factors after accounting for important nonmodifiable disease-related factors. It was hypothesized that disease-related, behavioral, and psychosocial factors would contribute in different ways to general, physical, and mental fatigue in PPS and that a portion of fatigue would be determined by potentially modifiable factors.

DESIGN

Cross-sectional study.

SETTING

A tertiary university-affiliated hospital post-polio clinic.

PATIENTS

Fifty-two ambulatory patients with PPS who were not severely depressed were included.

ASSESSMENT OF RISK FACTORS

Potential correlates for fatigue included disease-related factors (acute polio weakness, time since acute polio, PPS duration, muscle strength, pain, forced vital capacity, maximum inspiratory pressure, maximum expiratory pressure, body mass index, disability, fibromyalgia), behavioral factors (physical activity, sleep quality), and psychosocial factors (depression, stress, self-efficacy).

MAIN OUTCOME MEASUREMENTS

Fatigue was assessed with the Multidimensional Fatigue Inventory (MFI; assesses fatigue on 5 subscales) and the Fatigue Severity Scale (FSS).

RESULTS

Multivariate models were computed for MFI General, Physical, and Mental Fatigue. Age-adjusted multivariate models with nonmodifiable factors included the following predictors of (1) MFI General Fatigue: maximum inspiratory pressure, fibromyalgia, muscle strength; (2) MFI Physical Fatigue: maximum expiratory pressure, muscle strength, age, time since acute polio; and (3) MFI Mental Fatigue: none. The following potentially modifiable predictors made an additional contribution to the models: (1) MFI General Fatigue: stress, depression; (2) MFI Physical Fatigue: physical activity, pain; and (3) MFI Mental Fatigue: stress.

CONCLUSIONS

PPS fatigue is multidimensional. Different types of fatigue are determined by different variables. Potentially modifiable factors account for a portion of fatigue in PPS.

Post-polio syndrome: clinical manifestations and cerebrospinal fluid markers

Post-polio syndrome (PPS) refers to a constellation of new neurological, musculoskeletal and general symptoms occurring in survivors of poliomyelitis decades after acute paralytic and nonparalytic disease. The common manifestations of PPS include generalized, central and peripheral fatigue, muscle weakness and musculoskeletal pain. The pathogenesis of PPS remains obscure. Three prevailing hypotheses have been advanced: stress-induced degeneration of surviving neurons, persistent poliovirus replication or virus reactivation and immune-mediated damage. The diagnosis of PPS is based on medical history and clinical examination, since no specific diagnostic tests are available. In the light of recent studies demonstrating a partial beneficial effect of intravenous immunoglobulin, this article will focus on cerebrospinal fluid biomarkers reflecting disease activity and pathogenic processes in PPS.

Sleep-disordered breathing in fatigued postpoliomyelitis clinic patients

OBJECTIVE

To determine the frequency, predictive factors, and symptoms predictive of sleep-disordered breathing (SDB) in fatigued postpoliomyelitis clinic patients.

DESIGN

Cross-sectional, retrospective chart review.

SETTING

University-affiliated hospital postpolio clinic.

PARTICIPANTS

Postpolio clinic charts (N=590) were reviewed. Ninety-eight patients were included, and 492 patients were not included, primarily because of the lack of a polysomnogram.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE

The Apnea-Hypopnea Index (AHI) calculated as the total number of sleep-related breathing events/total sleep time.

RESULTS

The frequency of SDB defined by an AHI score of 5 or more was 65% and by an AHI score of 10 or more was 50%. Obstructive hypopnea was the predominant form, occurring in 86%. Age, sex, age at acute polio, time since polio, weakness and respiratory difficulties at acute polio, bulbar involvement at acute polio and at evaluation, body mass index, pulmonary function measures, alcohol use, sedative drug use, smoking, fibromyalgia, kyphoscoliosis, and scoliosis and ear-nose-throat surgery were not predictive of SDB (AHI scores > or =5 and > or =10). Snoring was more common in subjects with SDB (AHI score > or =5 and > or =10). Some pulmonary function measures correlated with oxygen saturation during sleep in SDB (AHI scores > or =5).

CONCLUSIONS

SDB was very common in fatigued postpoliomyelitis clinic patients referred for sleep evaluation. Obstructive hypopnea was the most frequent type. In this preliminary study, snoring tended to predict SDB.

Fatigue and neuromuscular diseases

PURPOSE

To identify the role of fatigue, its evaluation and its causes in the pathophysiology context of acquired or hereditary neuromuscular diseases of the spinal anterior horn cell, peripheral nerve, neuromuscular junction and muscle.

MATERIAL AND METHODS

A literature review has been done on Medline with the following keywords: neuromuscular disease, peripheral neuropathy, myopathy, fatigue assessment, exercise intolerance, force assessment, fatigue scale and questionnaire, then with the terms: Fatigue Severity Scale, Chalder Fatigue Scale, Fatigue Questionnaire, Piper Fatigue Scale, electromyography and the combination of the word Fatigue with the following terms: Amyotrophic Lateral Sclerosis (ALS), Post-Polio Syndrome (PPS), Guillain-Barre Syndrome, Immune Neuropathy, Charcot-Marie-Tooth Disease, Myasthenia Gravis (MG), Metabolic Myopathy, Mitochondrial Myopathy, Muscular Dystrophy, Facioscapulohumeral Dystrophy, Myotonic Dystrophy.

RESULTS

Fatigue is a symptom very frequently reported by patients. Fatigue is mainly evaluated by strength loss after an exercise, by change in electromyographic activity during a given exercise and by questionnaires that takes into account the subjective (psychological) part of fatigue. Due to the large diversity of motor disorders, there are multiple clinical expressions of fatigue that differ in their presentation, consequences and therapeutic approach.

CONCLUSION

This review shows that fatigue has to be taken into account in patients with neuromuscular diseases. In this context, pathophysiology of fatigue often implies the motor component but the disease evolution and the physical obligates of daily life also induce an important psychological component.

Cognitive functioning in post-polio patients with and without general fatigue

OBJECTIVE AND DESIGN

This study examined 2 main hypotheses. First, whether patients with post-polio suffering from general fatigue (n=10) demonstrate cognitive deficits compared with patients with post-polio without general fatigue (n=10). Secondly, by systematically varied test order administration we examined whether such differences varied as a function of increasing cognitive load during cognitive testing.

SUBJECTS

Twenty patients diagnosed with post-polio syndrome, 10 with general fatigue and 10 without fatigue.

RESULTS

Neither of the 2 hypotheses were confirmed. The group with general fatigue reported elevated levels of depression. However, no systematic association between level of depression and cognitive performance could be detected.

CONCLUSION

The results of this study provide no evidence that general fatigue or cognitive load affects cognitive functioning in post-polio.

Aging in polio

For a disease that was "conquered" some 40 years ago with the onset of effective vaccination, the issues of long-term survivors of paralytic polio as they age continue to present challenges to rehabilitation specialists. Aging with polio is a definition of PPS. There are over a million patients with PPS in the United States. Management has to include the appropriate use of exercises, appropriate bracing and support, and, in the case of bulbar and respiratory symptoms, the appropriate use of speech therapy services and ventilatory support. There are no prospective randomized trials studying the treatment of weakness and fatigue in PPS. Pharmacologic interventions are limited at this time but include anticholinergics for muscle weakness and dopaminergic agents or amantadine to control central fatigue. The pathophysiology of aging with polio is consistent with neuronal loss and denervation lying at the heart of the developing disorder, whereas the central nervous system components of the fatigue syndrome may be related to central changes with neuronal loss in the basal ganglia and reticular-activating system. Many of the survivors of the polio epidemics are in their later retirement years, and their needs will increase as they have other disabilities due to natural aging. Sensitivity to some of the special issues in PPS may help to avoid complications. Polio is an active infection in the third world. Although great strides have been made, the disease is endemic in eight nations and is threatening to spread. The lessons learned in treating PPS now will be useful in years to come as these individuals age and manifest PPS in the future.

Fatigue in neurological disorders

Chronic fatigue is a typical symptom of neurological diseases, and is most disabling in multiple sclerosis, postpoliomyelitis, poststroke, and in chronic fatigue syndrome. Disorders of neuromuscular junction transmission and metabolic diseases cause muscle fatigability, which is characterised by failure to sustain the force of muscle contraction (peripheral fatigue). Fatigue is also seen in diseases that affect the central, peripheral, and autonomic nervous systems (central fatigue). Enhanced perception of effort and limited endurance of sustained physical and mental activities are the main characteristics of central fatigue. Metabolic and structural lesions that disrupt the usual process of activation in pathways interconnecting the basal ganglia, thalamus, limbic system, and higher cortical centre are implicated in the pathophysiological process of central fatigue. A state of pre-existing relative hypocortisolaemia might sensitise the hypothalamic-pituitary-adrenal axis to development of persistent central fatigue after stress. The contributions of physiological, cognitive, and affective changes underlying fatigue are variable, and treatment is largely symptomatic and rehabilitative.

Le syndrome post-poliomyélitique

Postpoliomyelitis syndrome is a clinical syndrome characterized by late progression of symptoms, neuromuscular weakness, fatigue and pain, several (more than 20) Years after acute anterior poliomyelitis. In the United States, where it has been mainly described, frequency is estimated between 20 and 30p.100 in patients with sequelae of poliomyelitis. Although the cause is still unknown, postpoliomyelitis syndrome is likely due to degeneration and dysfunction of terminal axons of enlarged post-polio units, with a possible role of inflammatory reaction driven by persistence of the polio virus. Due to lack of specific therapy, rational therapeutic approaches are symptomatic, including exercise, reassurance and life-strategies for fatigue.

Varied clinical patterns, physical activities, muscle enzymes, electromyographic and histologic findings in patients with post-polio syndrome in Taiwan

STUDY DESIGN

A study of the clinical features, physical activity, muscle enzyme, electromyography and histopathological alternations of muscles in patients with post-polio syndrome (PPS).

OBJECTIVE

To assess the varied patterns of PPS in Taiwan.

SETTING

Taiwan.

METHODS

Thirty-one patients who fulfill the inclusion criteria of PPS were selected for study. Clinical features, physical activity scale, serum concentrations of creatine kinase, electromyography and histopathological alterations of muscles were assessed and correlated to the causes of PPS patients.

RESULTS

Patients with PPS in Taiwan are relatively young, with a mean age of 39.3 years. Elevated concentration of creatine kinase was found predominantly in male patients with higher physical activities. Electromyographic examinations as well as histological tests of affected muscles revealed prominent evidence of chronic and active denervation with reinnervation in PPS patients.

CONCLUSION

Patients with PPS in Taiwan are young. Thus, PPS should not be attributed to aging. Physical attrition with degradation of nerve terminals is considered the main cause of this disease.

SPONSORSHIP

This study was supported by the National Science Council, Republic of China under grant no. NSC-83-0412-B002-302.

Potential mechanisms in chemical intolerance and related conditions

The symptom of chemical intolerance may occur in isolation, but often occurs in conjunction with other chronic symptoms such as pain, fatigue, memory disturbances, etc. This frequent clustering of symptoms in individuals has led to the definition of several chronic multisymptom syndromes, such as multiple chemical sensitivity, fibromyalgia, chronic fatigue syndrome, and Gulf War illnesses. The aggregate research into these syndromes has suggested some unifying mechanisms that contribute to symptomatology. Multiple lines of evidence suggest that there is aberrant function of numerous efferent neural pathways, such as the autonomic nervous system and hypothalamic-pituitary axes, in subsets of individuals with these conditions. There is perhaps the greatest evidence for abnormal sensory processing in these syndromes, with a low "unpleasantness threshold" for multiple types of sensory stimuli. Psychological and behavioral factors are known to play a significant role in initiating or perpetuating symptoms in some persons with these illnesses. In the field of pain research, the interrelationship between physiologic and psychologic factors in symptom expression has been well studied. Using both established and novel methodologies, studies have suggested that psychologic factors such as hypervigilance and expectancy are playing a relatively minor role in most individuals with fibromyalgia and that clear evidence exists of physiologic amplification of sensory stimuli. These studies need to be extended to more sensory tasks and to larger numbers of subjects with related conditions. It is of note, though, that existing data on this spectrum of illnesses would suggest that there may be greater psychologic contributions to symptomatology if an illness is defined in part by behavior (e.g., avoidance of chemical exposures) rather than on the basis of symptoms alone.

Word finding difficulty as a post-polio sequelae

OBJECTIVE

Seventy-nine percent of respondents to the 1990 National Post-Polio Survey reported difficulty "thinking of words I want to say," with 37% reporting frequent, moderate-to-severe word finding difficulty. This study was undertaken to objectively document polio survivors' word finding difficulty and to identify its relationship to fatigue, neuropsychologic processes requiring cortical activation, and a peripheral marker for brain dopamine secretion.

DESIGN

In this study, 33 polio survivors were administered the Post-Polio Fatigue Questionnaire, Animal Naming and FAS Tests, and tests of attention and information processing speed. Plasma prolactin was also measured as a marker for brain dopamine secretion.

RESULTS

Subjects reporting high fatigue severity and word finding difficulty had clinically abnormal or significantly lower Animal Naming Test scores compared with subjects with low symptom severity. Impaired performance on the most difficult tests of attention and information processing speed were also associated with lower scores on the word finding tests. A significant negative correlation between Animal Naming Test scores and plasma prolactin suggests that a decrement in brain dopamine secretion is related to reduced animal naming ability.

CONCLUSIONS

These data support the hypothesis that decreased dopamine secretion, possibly secondary to poliovirus damage to the basal ganglia, may underlie not only fatigue and impaired attention but also word finding difficulty in polio survivors.

Nighttime sleep and daytime functioning (sleepiness and fatigue) in well-defined chronic rheumatic diseases

Wake/sleep complaints are very common in the rheumatic diseases, and include: insomnia, non-restorative sleep, frequent awakenings, daytime fatigue and excessive daytime sleepiness. Imprecise use of terminology has confused 'sleep dissatisfaction' (i.e. 'non-restorative sleep') with specific sleep disorders (i.e. 'insomnia' or 'sleep fragmentation') and 'fatigue' with 'daytime sleepiness'. This review examines current concepts from the literature of disparate disciplines pertaining to the complaint of poor sleep and daytime fatigue in patients with rheumatic disorders. The ability to monitor multiple physiologic parameters during sleep (polysomnography) has led to a greater understanding of normal and abnormal phenomena which occur during sleep, and has resulted in the identification of a variety of sleep disorders which have specific therapeutic implications. Actigraphy allows the prolonged monitoring of wake/sleep patterns, and the multiple sleep latency test permits the determination of physiologic sleepiness during the daytime. These techniques enable identification of objective sleep disorders in those whose complaint is subjective sleep dissatisfaction, and permit differentiation between the easily confused complaints of excessive daytime sleepiness and fatigue. The abnormal sleep/wake symptoms in patients with rheumatic diseases may not simply be a 'non-specific' or systemic effect of the disease. Some patients may have a specific sleep disorder (either independent from, or due to, the underlying rheumatic condition) which should be diagnosed and treated specifically. Conversely, subjective 'sleep dissatisfaction' does not necessarily imply an underlying sleep disorder. The primary intent of this review is to encourage systematic, objective study of sleep and daytime function in these common, often disabling conditions.

The symptoms of chronic fatigue syndrome are related to abnormal ion channel function

The pathogenesis of chronic fatigue syndrome (CFS) is unknown but one of the most characteristic features of the illness is fluctuation in symptoms which can be induced by physical and/or mental stress. Other conditions in which fluctuating fatigue occurs are caused by abnormal ion channels in the cell membrane. These include genetically determined channelopathies, e.g. hypokalemic periodic paralysis, episodic ataxia type 2 and acquired conditions such as neuromyotonia, myasthenic syndromes, multiple sclerosis and inflammatory demyelinating polyneuropathies. Our hypothesis is that abnormal ion channel function underlies the symptoms of CFS and this is supported also by the finding of abnormal cardiac-thallium201 SPECT scans in CFS, similar to that found in syndrome X, another disorder of ion channels. CFS and syndrome X can have identical clinical symptoms. CFS may begin after exposure to specific toxins which are known to produce abnormal sodium ion channels. Finally, in CFS, increased resting energy expenditure (REE) occurs, a state influenced by transmembrane ion transport. The hypothesis that ion channels are abnormal in CFS may help to explain the fluctuating fatigue and other symptoms.

Fibrillation potential amplitude after denervation

Fibrillation potentials have been reported to decline in amplitude with time after denervation. The use of maximum fibrillation potential amplitude to determine the relative acuity of axonal loss ("old" v "new/recurrent") has been advocated but with conflicting endorsements as to the appropriate benchmark amplitude, i.e., 100 microV compared with 250 microV. This investigation uses computer simulations to examine the rate of fibrillation potential amplitude decline expected given known values for muscle fiber size atrophy and conduction velocity slowing over time after denervation. Factors that affect the amplitude and potentially lead to erroneous interpretations in the clinical scenario of partially denervated muscle tissue are discussed. The use of fibrillation potential maximum amplitude criteria to determine the age of lesion onset in both totally and partially denervated muscle is fraught with technical and pathophysiological hazards of interpretation and must be considered cautiously, if at all, in clinical practice.

Abnormal movements in sleep as a post-polio sequelae

Nearly two-thirds of polio survivors report abnormal movements in sleep, with 52% reporting that their sleep is disturbed by these movements. Sleep studies were performed in seven polio survivors to document objectively abnormal movements in sleep. Two patients demonstrated generalized random myoclonus, with brief contractions and even ballistic movements of the arms and legs, slow repeated grasping movements of the hands, slow flexion of the arms, and contraction of the shoulder and pectoral muscles. Two other patients demonstrated periodic movements in sleep with muscle contractions and ballistic movements of the legs, two had periodic movements in sleep plus restless legs syndrome, and one had sleep starts involving only contraction of the arm muscles. Abnormal movements in sleep occurred in Stage II sleep in all patients, in Stage I in some patients, and could significantly disturb sleep architecture even though patients were totally unaware of muscle contractions. Poliovirus-induced damage to the spinal cord and brain is presented as a possible cause of abnormal movements in sleep. The diagnosis of post-polio fatigue, evaluation of abnormal movements in sleep, and management of abnormal movements in sleep using benzodiazepines or dopamimetic agents are described.

Management of postpolio syndrome

Recent research has shed light on the pathogenesis of the postpolio syndrome and has helped explain its symptoms and the rationale for management. The aim of this article is to familiarize physicians with this syndrome. The history, acute infection, definition, and diagnosis are discussed, as well as the various symptoms and their management. People with postpolio syndrome can educate health professionals about this condition and can help others inflicted with this syndrome. Thus far, no cure is available. A correct diagnosis is important, and the physician must realize that severe comorbidities tend to afflict people with this syndrome. Numerous management options are available to help these people enjoy a high quality of life.

Bromocriptine in the treatment of post-polio fatigue: a pilot study with implications for the pathophysiology of fatigue

Fatigue is the most commonly reported and most disabling of all post-polio sequelae (PPS). Bromocriptine mesylate (Parlodel) was employed in a placebo-controlled trial in five survivors of paralytic polio who continued to report moderate to severe daily fatigue after complying with the conservative treatments prescribed for PPS. Placebo was given for 4 wk followed by increasing doses of bromocriptine mesylate, administered at 12:00 pm for 28 days, which reached a total dose of 12.5 mg/day. Three subjects reported marked symptom improvement on bromocriptine but not on placebo. Their reported difficulty with attention, concentration, word finding, mind wandering, memory, thinking clearly, and fatigue on awakening was significantly negatively correlated with days on bromocriptine but not with days on placebo. Before the drug trial began, responders had clinically impaired performance on neuropsychologic tests of attention and information processing speed, more than twice as many hyperintensities on magnetic resonance imaging of the brain, abnormally low fasting adrenocorticotropic hormone levels, and nearly double the mean plasma prolactin level compared with nonresponders. The implications of these findings for the pathophysiology of fatigue are discussed. A double-blind, placebo-controlled, multicenter study will be needed to confirm bromocriptine's efficacy in treating attentionally and neurophysiologically impaired polio survivors whose severe and disabling fatigue does not respond to conservative therapies.