Dementia Associated with Sensorimotor Signs

A third major pattern in dementia is one in which cognitive decline is accompanied by sensory and motor signs. Most often, the salient mental state changes of these dementias also involve complex attention, behavior, and personality. Changes in executive functions are not universal, but depend on where the brunt of the neuropathology is located. Table 7 lists a number of disease processes that tend to have this dementia profile. The disease entity in this category with the highest prevalence is vascular dementia. Unfortunately, it is not uncommon for clinicians to "automatically" render the diagnosis of vascular dementia after a demented patient's MRI or CT scan returns with some evidence of strokes or small vessel disease. Many autopsy series suggest that the accuracy of clinical diagnoses of vascular dementia can be quite low (21-82%) (103,104). A large per-

Table 7

Dementias Associated With Sensorimotor Signs

Vascular dementia

Infection (e.g., HIV, syphilis, Creutzfeldt-Jacob disease) Metabolic abnormalities (e.g., B12 deficiency)

Inherited disorders of metabolism (e.g., metachromatic leukodystrophy, Kuf's disease) Normal pressure hydrocephalus Multiple sclerosis

Inflammatory/autoimmune disease (e.g., SLE)

Degenerative diseases with extrapyramidal features (e.g., Parkinson's disease, Huntington's disease, progressive supranuclear palsy, and Wilson's disease) Motor neuron disease with frontotemporal dementia centage of patients diagnosed with vascular dementia are determined at autopsy to have Alzheimer's pathology, with or without significant cerebrovascular insults (105,106). Although earlier reports of the prevalence of vascular dementia varied widely, recent reviews suggest a prevalence in the United States of around 10% (15,70,107). Symptoms of dementia are reportedly more likely to develop after a critical volume of tissue is infarcted (over 50 mL) or if small strokes are strategically placed that disrupt cognitive abilities (108). Table 8 summarizes the DSM-IV diagnostic criteria for vascular dementia. Diagnosis of vascular dementia is supported by the sudden development of impairments in one or more cognitive domains, a stepwise deteriorating course, focal neurological signs, risk factors for stroke, and a history or imaging evidence of strokes.

If a patient has a history of an insidiously progressive amnestic dementia and is found to have a stroke with sensorimotor signs, a clinician should still consider the diagnosis Alzheimer's disease as likely, but recognize that the cerebrovascular disease may be making an additional contribution to the patient's cognitive impairments. Strokes may reduce "cognitive reserve" in patients and lead to earlier, more dramatic presentations of clinical problems in patients with underlying AD pathology (109). A diagnosis of vascular dementia is probably most tenuous in a demented patient with prominent memory problems, no history suggestive of clinical strokes, and an MRI scan that reveals mild white matter changes and a few T2 signal abnormalities.

As noted on Table 7, there are numerous dementias that are associated with sensorimotor signs of which we will briefly mention HIV associated dementia, neurosyphilis, normal pressure hydrocephalus, multiple sclerosis, and extrapyramidal syndromes. These dementias tend to present with apathy, social withdrawal, blunted affect, diminished behavioral output, and compromised attention. For example, changes in mental state changes can be the presenting

symptoms of HIV infection, although much more commonly there are systemic signs to point to this diagnosis (110,111). Peripheral neuropathy and myelopathy are also commonly seen in HIV infection. The pathology associated with tertiary syphilis tends to be most severe in the frontal and temporal lobes, with associated personality changes, impaired judgment, and altered mood (112,113). Sensorimotor abnormalities commonly accompany the dementia, including dysarthria and changes in gait and reflexes.

Normal pressure hydrocephalus (NPH) is believed to account for about 10% of the reversible dementing illnesses (36). The well-known triad associated with NPH includes gait disturbance, incontinence, and progressive decline in cognitive functioning (114). The pattern of mental state changes seen in NPH usually involves slowed processing speed, impaired complex attention, and diminished executive functioning (115-117). Aphasia and apraxia are unusual and would suggest other contributing etiologies. There is ongoing debate about the best strategies for identifying patients who will benefit most from the placement of a shunt. Normal-sized sulci, periventricular edema, CSF flow void on MRI in the cerebral aqueduct, third and fourth ventricles, and clinical response to the removal of approximately 30 mL of CSF have been reported to be predictive of better outcomes (118-120). Cisternography does not appear to add much to the information obtained by clinical history and imaging studies (121).

Patients with multiple sclerosis often suffer from cognitive, emotional, and behavioral problems that tend to add to their disability and problems functioning at home and work (122-124). Dementia has been reported in up to a third of patients with Parkinson's disease (125-128). Some patients have coexisting Alzheimer's pathology, which probably accounts for their decline in mental state functioning. Others present with a disruption of frontal networks ("subcortical dementia syndrome") with bradyphrenia, impaired activation, and forgetfulness. These difficulties may reflect diminished dopamine availability to caudate nucleus and prefrontal regions. Medications and coexisting depression also may play an important role. Huntington's disease, progressive supranuclear palsy, and Wilson's disease all have associated mental state changes, which in part reflect the disruption of frontal networks (89,129-136). The associated extrapyramidal features tend to point to the diagnosis in these cases. From 2% to 3% of patients with motor neuron disease present with dementia that has nearly identical features to the frontotemporal dementia that was described earlier (137,138).

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