Retrogenesis: clinical, physiologic, and pathologic mechanisms in brain aging, Alzheimer's and other dementing processes

Data from clinical, electrophysiologic, neurophysiologic, neuroimaging and neuropathologic sources indicates that the progression of brain aging and Alzheimer's disease (AD) deterioration proceeds inversely to human ontogenic acquisition patterns. A word for this process of degenerative developmental recapitulation, "retrogenesis", has been proposed. These retrogenic processes provide new insights into the pathologic mechanism of AD deterioration. An understanding of retrogenic phenonmena can also result in insights into the applicability of retrogenic pathologic mechanisms for non-AD dementing disorders. Management strategies based upon retrogenesis have recently been proposed. Retrogenic pathophysiology also points to previously unexplored pharmacologic approaches to dementia prevention and treatment.

Equilibrium and limb coordination in mild cognitive impairment and mild Alzheimer's disease

OBJECTIVE

To examine changes in equilibrium and limb coordination in normal aging, mild cognitive impairment, and moderate cognitive impairment associated with early probable Alzheimer's disease (AD), by means of parametric clinical measures.

DESIGN

Case series

SETTING

Out-patient clinic.

PARTICIPANTS

A consecutive sample of 365 community-residing ambulatory volunteers (137 men, 228 women; mean age 70.4 +/- 9.4 years; mean educational attainment 14.6 +/- 3.1 years), who were followed in an ongoing longitudinal study of aging and AD, comprising cognitively intact individuals, persons with mild cognitive impairment, and patients with mild AD.

MEASUREMENTS

For general magnitude of cognitive function, the Global Deterioration Scale (GDS). For cognition, the Mini-Mental State Examination (MMSE). Equilibrium was assessed with parametric measurements of single leg stance (SLS) and tandem walking (TW). Limb coordination was assessed with parametric measurements of foot tapping (FT), alternating pronation and supination (PS), and sequential finger to thumb tapping (FTH).

MAIN RESULTS

After adjustment for age, persons with mild cognitive impairment or mild AD had significantly poorer performance on parametric clinical tests of equilibrium and limb coordination compared with cognitively intact individuals (P < .05).

CONCLUSIONS

Changes in equilibrium and limb coordination are clinically demonstrable in persons with mild cognitive impairment and mild AD using simple parametric tests. Such tests could potentially identify individuals with increased risk of falling. Early diagnosis and treatment of conditions that can jeopardize equilibrium and limb coordination, as well as balance and coordination training, might help cognitively impaired older people to maintain optimal function and may decrease the risk of falls and injuries.

Towards a science of Alzheimer's disease management: a model based upon current knowledge of retrogenesis

BACKGROUND

General relationships between dotage and infancy and childhood have been acknowledged for more than two millennia. Recent findings indicate precise relationships between functional, praxic, and feeding changes in the course of the degenerative dementia of Alzheimer's disease (AD) and inverse corresponding developmental sequences. Similar inverse relationships between AD and human development can be described for cognition and language skills; for physiologic measures of electroencephalographic activity, brain glucose metabolism, and developmental neurologic reflex changes; and for the neuropathologic and neuroanatomic progression of these processes. In AD, these processes may be termed "retrogenesis." The relevance of the retrogenesis model for AD management is explored.

METHOD

The functional stages of AD can be translated into developmental age equivalents that can be utilized to explicate observed changes in the disease.

RESULTS

The retrogenesis-based developmental age model can usefully inform an understanding of the general care needs, emotional and behavioral changes, and activity needs of the AD patient. This model must be amended by necessary caveats regarding physical differences, variations in age-associated pathology, differences in social and societal reactions, and differences in background between AD patients and their developmental age "peers."

CONCLUSIONS

Knowledge of retrogenesis and the developmental age of the AD patient can form a nidus for the development of a nascent science of disease management. Such a science must ultimately incorporate not only appropriate caveats but also relevant universal human needs, such as those for dignity, love, and movement.

Progression of Alzheimer's disease: variability and consistency: ontogenic models, their applicability and relevance

Much has been learned about the clinical symptomatology of Alzheimer's disease (AD) and ontogenic reciprocal relationships in the past few decades. It is now possible to describe and verify inexorable symptomatic sequences and corresponding temporal relationships. It is also possible to identify more variable symptoms in AD. Ontogenic models can be useful in providing a clearer understanding of the nature of AD symptomatology in terms of both consistency and variability. These models can also be informative in explicating the management needs of AD patients and the treatment possibilities of AD symptoms as well as the etiology of variability in AD symptoms.

Neurologic markers of the progression of Alzheimer's disease

This article describes the results of studies conducted to determine the usefulness of reflex changes as markers of disease severity in Alzheimer's disease (AD). Standardized and quantified muscle stretch reflexes, cutaneous reflexes, and developmental (primitive) reflexes were studied in normal older adults, in individuals with mild memory impairment, and in patients with AD, in all clinical severity stages as assessed with the Global Deterioration Scale (GDS), the Mini-Mental State Examination (MMSE), and the Functional Assessment Staging (FAST) procedure. Changes in frequency and intensity of these individual reflex variables, as well as of variables consisting of combinations of these individual reflexes, appeared to be sensitive indicators of the progression of AD. These neurological reflex variables showed high Pearson correlations with the GDS (.72), the MMSE (.74), and the FAST (.80). Standardized quantified neurological reflex measures are useful as noncognitive, education-independent, and culture-independent markers of the course of AD.

Neuromotor changes in Alzheimer's disease: implications for patient care

As a result of the neuropathologic process of Alzheimer's disease (AD), significant changes occur in neuromotor function (e.g., paratonia and compulsive grasping). These changes become manifest in the moderately severe stage of AD, when patients begin to require ongoing assistance with activities of daily life (ADL), and they are prominent in the severe stage of AD, when patients are continuously dependent on a caregiver. Patients in these stages often display behavioral disturbances during care activities. These disturbing behaviors result not only from cognitive impairment, but also from a patient's physical inability to cooperate with the caregiver. When care management strategies take into account the characteristic physical restrictions resulting from the neuromotor changes that accompany advanced AD, the caregiving process may be significantly facilitated.

Utility of developmental reflexes in the differential diagnosis and prognosis of incontinence in Alzheimer's disease

Four developmental reflexes, the tactile suck reflex, the palmar and plantar grasp reflexes, and the plantar extensor reflex, were examined in 784 individuals, including healthy elderly, cognitively and functionally mildly impaired individuals, and patients with Alzheimer's disease (AD) in all stages of clinical severity. The study population was classified into six categories of increasingly impaired functional performance, and prevalence of the four individual reflexes and of a summary reflex measure, consisting of a combination of these four reflexes, was determined for each category. Prevalence of all five reflex measures was more than six times higher for those categories that comprised only permanently doubly incontinent patients as compared to those categories that comprised only continent individuals (P < .001). Frequency of developmental reflexes rose sharply with the onset of progressive incontinence. Since the return of these reflexes in AD is associated with severe cortical dysfunction, it is concluded that these developmental reflexes are useful in differentiating incontinence of cortical origin from incontinence resulting from potentially reversible causes.

Mortality and temporal course of probable Alzheimer's disease: a 5-year prospective study

Alzheimer's disease (AD) is associated with an increased mortality in comparison with aged control populations. The relationship between the clinical and the temporal course of AD has not been well studied over significant intervals. Community-residing patients with probable AD (N = 103, 42 men, mean age = 70.2 +/- 8.0 years) were studied at baseline on demographic and clinical variables, including measures of global deterioration (Global Deterioration Scale; GDS), mental status and cognition (e.g., Mini-Mental State Examination; MMSE), and functional impairment (Functional Assessment Staging; FAST). Baseline characteristics included a GDS range of Stage 4, 5, or 6 (38.8%, 39.8%, and 21.4%, respectively) and a mean MMSE score of 15.4 +/- 5.6. The mean follow-up interval was 4.6 +/- 1.4 years. Follow-ups were done blind to baseline measures and when necessary were conducted in residential and nursing home settings. Of locatable subjects (n = 95, 92%), 30 (31.6%) were decreased. Survivors (n = 65) had a mean GDS stage of 6.2 +/- 0.9 and a mean MMSE score of 5.1 +/- 6.9; 51% had MMSE scores of 0. Increased age and male gender, but not baseline clinical dementia variables, increased the risk of death (ps < .01). Change in clinical variables correlated significantly with time elapsed (r = .32, p < .05, for MMSE change, to r = .48, p < .001, for GDS change). Significant variance in temporal change (i.e., time elapsed) was accounted for by change in two of the five clinical measures studied (i.e., GDS and FAST; multiple r = .53). The results support previous estimates of mean duration of the GDS and FAST stages. For subjects with probable AD followed over approximately 5 years, clinical variables changed significantly over time in survivors. However, the majority of temporal variance in the course of AD remains unexplained.

Overview of methodologic issues for pharmacologic trials in mild, moderate, and severe Alzheimer's disease

To address the issue of mild, moderate, and severe Alzheimer's disease (AD), it is necessary to initially establish some agreement on terminology. In recent decades, these terms have frequently been defined using screening instrument scores with measures such as the Mini-Mental State Examination (MMSE). There are many problems with this approach, perhaps the most salient of which is that it has contributed to the total and tragic neglect of patients with severe AD. An alternative approach to the classification of AD severity is staging. This approach has advanced to the point where moderately severe and severe AD can be described in detail. Procedures for describing this previously neglected latter portion of AD have recently been extensively validated. Staging is also uniquely useful at the other end of the severity spectrum, in differentiating early aging brain/behavior changes, incipient AD, and mild AD. Temporally, with staging procedures, it is possible to track the course of AD approximately three times more accurately than with the MMSE. The net result of the advances in AD delineation is that issues such as prophylaxis, modification of course, treatment of behavioral disturbances, loss of ambulation, progressive rigidity, and the development of contractures in AD patients can now be addressed in a scientifically meaningful way that will hopefully bestow much benefit in AD patients and those who care for them.

Contractures and loss of function in patients with Alzheimer's disease

OBJECTIVE

To investigate the prevalence of contractures in patients with Alzheimer's disease and to assess possible associations between contractures and cognitive and functional decline in Alzheimer's disease.

DESIGN

Case series.

SETTING

Subjects from an outpatient, university-based, dementia research center, followed, when necessary, into residential home and nursing home settings.

PATIENTS

A consecutive sample of 161 patients (48 men, 113 women; mean age 75.3 +/- 8.6 years) with a clinical diagnosis of probable Alzheimer's disease and with deficits in basic activities of daily living or more severe functional impairment.

MAIN OUTCOME MEASURES

For cognition, the Mini-Mental State Examination (MMSE); for functioning, the Functional Assessment Staging Scale (FAST); contracture is defined as a decrease of 50% or more of the normal passive range of motion of the joint.

RESULTS

Prevalence of contractures was correlated highly with degree of functional impairment (r = .70, P < .001). More than three quarters of patients who had lost the ability to walk manifested contractures; however, contractures were found in fewer than 11% of all ambulatory patients examined. When present, contractures involved more than one extremity in 97% of cases and involved all four extremities in more than two-thirds of patients.

CONCLUSION

Joint contractures are very common in the severe stages of Alzheimer's disease. More than a quarter of a million institutionalized residents in US nursing homes are likely to be afflicted by this potentially painful and disfiguring condition. Possible pathophysiology and contributing factors and possible means of intervention for this major source of disability are discussed.

The neurologic syndrome of severe Alzheimer's disease. Relationship to functional decline

OBJECTIVE

To assess the possible association between functional decline and noncognitive neurologic signs in the severe stages of Alzheimer's disease (AD).

DESIGN

Case series.

SETTING

Subjects from a dementia research referral center, longitudinally followed, when necessary, into residential home and nursing home settings.

PATIENTS

A consecutive sample of 56 patients (16 men, 40 women; mean age, 74.6 years) with a clinical diagnosis of probable AD in the moderately severe and severe stages.

MAIN OUTCOME MEASURE

For global dementia severity, the Global Deterioration Scale and Mini-Mental State examination; for functional assessment, the Functional Assessment Staging Scale; and for assessment of neurologic function, nine release signs (primitive reflexes), 10 measures of extrapyramidal function, and five measures of pyramidal function, including deep-tendon reflexes and plantar signs. Changes in activity or presence of neurologic signs were rated on a seven-point scale. Results were analyzed in terms of prevalence and magnitude of change in relation to functional impairment.

RESULTS

Prevalence and mean scores of certain release signs, certain extrapyramidal measures commonly referred to as bradykinesia, and certain pyramidal signs showed significant associations with the magnitude of functional impairment. Other neurologic measures, for example, the palmomental reflex, and certain extrapyramidal measures commonly seen in Parkinson's disease, including the glabellar blink reflex, cogwheeling, tremor, shuffling gait, and festination, did not show significant increments with continuing functional decline in AD.

CONCLUSIONS

Functional decline in the advanced stages of AD appears to be associated with a particular combination of progressive cortical, extrapyramidal, and pyramidal system dysfunction. The characteristics of this neurologic syndrome of the severe stages of AD differ from those of other neurologic disorders. For example, the pattern of extrapyramidal system disease is different from that seen in Parkinson's disease. The neurologic syndrome of the severe stages of AD is amenable to description and deserves further investigation.

Cognition-independent neurologic symptoms in normal aging and probable Alzheimer's disease

Deep tendon reflexes, plantar responses, muscle tone, and release signs were studied as 14 individual clinical variables and as five summary variables in 135 aged subjects, including 27 control subjects, 20 subjects with mild cognitive impairment, and 88 subjects with successive stages of probable Alzheimer's disease. Changes in activity of elicited responses were rated on a seven-point scale. Results were analyzed both as prevalence and mean degree of change in activity. Rating on a variable combining all 14 individual variables was significantly higher in a group with mild cognitive impairment than in a control group. Subjects with an early stage of Alzheimer's disease had both higher prevalence of increased activity and increased mean scores of deep tendon reflexes and muscle tone. They had a higher prevalence of increased activity on a variable combining three release signs. Patients with a late stage of Alzheimer's disease had significantly increased prevalence and mean scores of muscle tone and grasping and sucking reflexes compared with control subjects and patients with the early stage of Alzheimer's disease.

Dementia in an American-Chinese nursing home population

Of 58 demented residents in an American-Chinese nursing home, 44 (75.9%) had multi-infarct dementia, seven (12.1%) had possible Alzheimer's disease, four (6.9%) had other dementias, and three 5.2% had unknown disorders. Alzheimer's disease was relatively less prevalent than in U.S. nursing homes overall.