Differential diagnosis of delirium
The myth of ICU psychosis. ICU psychosis belongs with the hydra, Medusa, or any other mythological creature. People indeed become delirious in the ICU, but this has nothing to do with the ICU. One does not refer to Lazy Chair psychosis when a nursing home patient becomes delirious as a result of a urinary tract infection. The main problem with the phrase 'ICU psychosis' is that suggests merely moving a patient out of the ICU will fix the problem. More importantly, it suggests that there is no need to search for the underlying cause of the delirium. If either of these suggestions are taken to heart, the patient could die.
The differential diagnosis of delirium can be very challenging, especially in the medically complicated patients. A major issue to recognize is the importance of recognizing emergent conditions that require more than psychiatric care. Though mnemonics are largely detestable, one that is often used is WHHHHIMP:
- Wernicke's encephalopathy or Withdrawal
- Hypoxia, Hypertensive encephalopathy, Hypoglycemia, Hypoperfusion
- Intracranial bleeding or infection
- Meningitis or encephalitis
- Poisons or medications
See why mnemonics are so bad? That one should really be WWHHHHIIMEPM.
Exclusionary diagnoses
To make the diagnosis of delirium, several conditions need to be ruled out:
- Dementia. The time course of the symptoms along with the past medical and psychiatric history will usually differentiate between the two. For example, delirium would be acute as opposed to slowly progressive; fluctuating rather than stable symptoms. It can be challenging to rule out Creutzfelt-Jakob disease as its onset is typically rapid, though often not as acute as delirium.
- Aphasia. If the aphasia results from stroke, then impairment in other areas should be more limited than in delirium.
- Acute psychosis, mania. In acute exacerbations of psychiatric illness, thought disorders are usually better organized than in delirium. Mood abnormalities would be pronounced and hallucinations are more likely to be auditory than visual.
Assessment of delirium
For a complete workup of delirium,medical and neuropsychiatric assessment must be complete.
★ One of the most sensitive indicators of delirium is handwriting impairment. The impaired ability to draw a clock is also an indicator of cognitive dysfunction. Ideally, one can use the 10-Point Clock Test as a more objective measure.
★★ The practice guidelines for treating delirium are a decade old, but provide a valuable checklist for assessing a delirious patient.
Etiologies
Common etiologies of delirium include infection, medications, withdrawal syndromes, hypoxia, electrolyte disturbances, surgery, cancer, cardiovascular disease, and serotonin syndrome.
Bacteremia has strong associations with encephalopathy. Interestingly, approximately 30% of patients over the age of 50 with urinary tract infections present with confusion. Many people are familiar with the classic delirium case of, say, an 85 y/o frail female with a urinary tract infection.
★Without exception, the sudden onset of confusion or agitation in an older patient should cause one to rule out infection first.
Some studies have reported that approximately 40% of the cases of delirium are due to medications. Almost any medication can induce delirium, though some are more strongly associated than others. Even medications a patient has been stable on for some time can lead to delirium in the context of medical illness.
It is important to assess not only regular medications, put prn medications as well. Medications that are more commonly associated with delirium are listed here.
It is always important to be alert for withdrawal symptoms as they can be challenging to detect in the context of medical illness. In particular, seizures, unexplained autonomic arousal could suggest withdrawal. However, autonomic arousal may be masked by underlying hypertension. It is important to look for any history of alcohol or substance abuse.
Whenever a
patient exhibits mental status changes, it is important to assess oxygen
saturation. Although common lore is that alertness is an indicator of
oxygenation, that is not always the case: Alertness can be preserved during moderate hypoxemia. The reason for this is
that the rate of development of hypoxemia is a determining factor of function.
It is like boiling a frog. If you put the frog in boiling water it jumps out.
If you put the frog in cold water and turn up the heat, it is cooked. (Note
that this is not the preferred method
In patients with chronic hypoxia, saturations as low as 60mm Hg can produce very little change. However, if a patient is accustomed to higher levels, small changes can result in delirium.
Thyroid imbalance
Hypothyroidism is classically associated with depression and anxiety. Such patients will often have a history of thyroid ablation in the past. For psychiatric consultations regarding depression, thyroid function tests should probably be obtained on most, if not all, patients. Thyroid stimulating hormone is considered to be a very sensitive indicator of thyroid function. If the patients found to be hypothyroid, he or she usually responds quite well when thyroid augmentation is started and the patient is given time to stabilize.
Hyperthyroidism can present with anxiety, sweating, tremor, or racing thoughts. In some cases, although it is not classic, hyperthyroidism can result in depression as well.
Electrolyte disturbances
Electrolyte disturbances can lead to a wide range of psychiatric symptoms. A summary of these issues is provided in this table. It is important to always check laboratory values.
Surgery
There are several risk factors that can be identified for delirium after surgery. Preoperatively, advanced age, dementia, severe preoperative illness, depression, and family history of psychiatric illness all increase the risk of post-operative delirium. Lengthy surgeries, increased transfusion requirements, and the type of surgery can increase the risk of delirium.
Cancer
Delirium is fairly common among patients with cancer. In a prospective series of cancer patients admitted to a palliative care unit, 42% were delirious on admission, and delirium developed later in 27%. Fortunately, the delirium was a reversible in about half of the patients.
★Brain metastases may present as depressed mood, confusion or forgetfulness without any other neurological signs. In terms of tumors that metastasize to the brain, in decreasing order of frequency they are:
- Lung
- Breast
- Melanoma
- Colon
- Rectum
- Kidney
When they are not the result of metastases, effects of cancer that produce mental status changes are referred to paraneoplastic limbic encephalopathy (PLE). This name derives from limbic changes that result from a non-brain tumor. PLE can appear as dementia-like syndromes, anxiety, depression, and/or psychosis. PLE occurs most commonly with lung cancer. In DSM-IVTR terms, PLE would be delirium due to a general medical condition.
Cardiovascular disease
There is a high incidence of delirium in patients with cardiovascular disease. Sometimes CNS hypoperfusion (resulting from congestive heart failure, MI, stroke, hypovolemia, or hypotension caused by medications) gives rise to delirium. Other causes in this population include medications and general medical conditions.
Serotonin syndrome
Serotonin syndrome has causes other than the combination of an SSRI with an MAOI. Drugs that have been associated with serotonin syndrome include: SSRI's, tricyclic antidepressants, antiemetics (e.g., odansetron), sumatriptan, lithium, meperidine, tramadol, fentanyl, dextromethorphan, amphetamines, cocaine, bromocriptine, and sibutramine.