Dementia

 Dementia is caused by progressive, irreversible degener-ation of the cerebral cortex and results in mental deterio-ration, usually over several years. There is gradual impairment of memory (especially short term), intellect and reasoning but consciousness is not affected. Emo-tional lability and personality change may also occur. 
Alzheimer's disease 
This condition is the commonest form of dementia in developed countries. The aetiology is unknown although genetic factors may be involved. Females are affected twice as often as males and it usually affects those over 60 years, the incidence increasing with age. There is pro-gressive atrophy of the cerebral cortex accompanied by deteriorating mental functioning. Death usually occurs between 2 and 8 years after onset. 
Huntington's disease
 This usually manifests itself between the ages of 30 and 50 years. It is inherited as an autosomal dominant disor-der  associated with deficient production of the neurotransmitter gamma aminobutyric acid (GABA). By the time of onset, the individual may have passed the genetic abnormality on to their children. Extrapyramidal changes cause chorea, rapid uncoordinated jerking movements of the limbs and involuntary twitching of the facial muscles. As the disease progresses, cortical atrophy causes personality changes and dementia. 
Secondary dementias 
Dementia may occur in association with other diseases:
 • cerebrovascular disease, e.g. multi-infarct dementia
 • infections, e.g. neurosyphilis, human immunodeficiency virus (HIV), Creutzfeldt-Jakob disease
 • cerebral trauma
 • alcoholism and some drugs
 • vitamin B deficiencies
 • metabolic disorders, e.g. hypothyroidism, uraemia, liver failure. 

Parkinson's disease 07.18 In this disease there is gradual degeneration of dopa.. mine releasing neurones in the extrapyramidal system, This leads to lack of control and coordination of muscle movement resulting in: 
• slowness of movement (bradykinesia) and difficulty initiating movements 
• fixed muscle tone causing expressionless facial features, rigidity of voluntary muscles causing the slow and characteristic stiff shuffling gait and stooping posture 
• muscle tremor of extremities that usually begins in one hand, e.g. 'pill rolling' movement of the fingers. Onset is usually between 45 and ki years. The cause is usu-ally unknown but some cases are associated with repeated trauma as in, e.g., 'punch drunk' boxers; tumours causing midbrain compression; drugs, e.g. phenothiazines; heavy: metal poisoning. There is progressive physical disability but the intellect is not impaired .