Hypothyroidism is suggested by cold intolerance, heavy menstrual bleeding, slow speech, loss of lateral margins of eyebrows, coarse hair, dry skin, slow ankle jerks in the relaxation phase, Bradycardia,
B-12 deficiency is suggested by an abnormal blood count showing anemia and macrocytosis, the patient may have features of subacute combined degeneration of cord, this is manifested by absent knee jerks but extensor plantar reflex. Beefy red tongue is another pointer. Also think about it in someone who had ileal resectio (Distal ileum is site of absorption) or had a gastrectomy (Intrinsic factor gets produced in the stomach).
Liver dysfunction is suggested by the history of alcohol intake, hepatitis, presence of jaundice, hepatomegaly or ascites. Dementia may be due to direct damage by alcohol, or cirrhosis related hepatic encephalopathy. The first symptom of hepatic encephalopathy is altered sleep pattern - e.g sleeping during the day and staying awake at night.
Renal dysfunction does not have many clinical features but a simple serum chemistry test would reveal the answer.
Drug toxicities which may be related to illicit drug usage or medications that the patient is taking and the levels of these might be abnormal. Examples include paint thinner, Anti-seizure meds, psychotropic drugs, sedatives and narcotics .
Subdural hematoma is suggested by waxing and waning of mental status and alertness. The history of a recent fall in an elderly person certainly gives a good lead.
Syphilis in its tertiary phase can give dementia and is suggested by the presence of Rhomberg's sign - which suggests the degeneration of the posterior column just like in B-12 deficiency.
HIV must be thought of in the presence of lymphadenopathy as persistent glandular lymphadenopathy is the commonest feature of HIV. The history of illicit drug usage or multiple sexual encounters gives further leads. One may look for needle track marks in the elbows and legs.
Brain tumors are manifested typically by the presence of focal signs. One should always remember false localizing signs for instance sixth nerve palsy (lateral rectus palsy) & papiledema.
Encephalopathies secondary to infection can be detected by history of some infection going on for instance urinary tract infection. Sometimes but rarely a primary encephalitis may be the cause of abnormal mental status but this is usually an acute event and is classified as delirium instead of dementia.
Multi-infarct dementia is similar to Alzheimer's type but has multile lacunar infarcts seen on CT scan and the Affect is Labile - meaning that one minute the patient is laughing and the next is crying or angry.
Alzheimers dementia is the commonest variety of dementia and occurs after age 60. Premature dementia of this type is seen in Downs syndrome (trisomy 21), trisomy 22 and familial dementia. Most cases have no obvious cause. High dose Ibuprofen is the only drug known to prevent it. CT shows cerebral atrophy and There are structural changes associated with it. These are senile plaques and neurofibrllary tangles (but these are seen in other disorders too). They are most common in the temporal lobe structures, such as the hippocampus and amygdala.