Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (87 page)
Authors: Mary A. Williamson Mt(ascp) Phd,L. Michael Snyder Md
In elderly patients and in patients with medical illness, delirium and confusional states are not uncommon. The diagnosis of delirium requires that the practitioner recognize that delirium is present, a thorough history and physical examination, neurologic examination, and testing to determine the underlying etiology. The differential diagnosis includes sun downing, nonconvulsive status epilepticus, dementia, primary psychiatric illness, and focal syndromes such as Wernicke aphasia, Anton syndrome, and brain tumor particularly in the frontal lobe.
Laboratory Findings
Targeted testing is recommended based on the history and physical. General screening tests should include electrolytes, creatinine, glucose, calcium, CBC, and urinalysis. Appropriate drug levels should be ordered. Delirium may occur even with therapeutic drug levels of digoxin, lithium, or quinidine. Blood and urine toxicology screens should be considered. Blood gas analysis to rule out hypoxia, respiratory alkalosis (which may be seen in sepsis, hepatic failure, or cardiopulmonary disease), and metabolic acidosis is helpful. Liver function tests may be contributory in patients with a history of alcoholism or liver disease. Thyroid function and vitamin B
12
may be helpful in patients with a history of cognitive decline over several months.
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Suggested Readings
1. American Psychiatric Association.
Diagnostic and Statistical Manual
, 4th ed. Washington, DC: APA Press; 1994.
2. Plaschke K, von Haken R, Scholz M, et al. Comparison of the confusion assessment method for the intensive care unit (CAM-ICU) with the Intensive Care Delirium Screening Checklist (ICDSC) for delirium in critical care patients gives high agreement rate(s).
Intensive Care Med.
2008;34:431.
DISORDERS WITH FOCAL NEUROLOGIC DEFICITS
(NEUROPATHIES)
Disorders of the peripheral nerve system include polyneuropathies, mononeuropathies, and mononeuropathy multiplex (multiple mononeuropathies). The etiology of each of these is varied and includes systemic illnesses, toxins, or genetic abnormalities. The distinction between central nervous system disorders and peripheral nerve or muscle diseases can be made on clinical assessment with help from various diagnostic modalities including EEG, EMG, blood tests, genetic testing, and muscle or nerve biopsy. The involvement of a single limb, especially if with pain, suggests a peripheral neuropathy. This section reviews the major categories and several of the more common individual disorders.
POLYNEUROPATHY (NEURITIS/NEUROPATHY, MULTIPLE)
Polyneuropathy is a generalized, homogeneous process affecting multiple peripheral nerves. Polyneuropathy must be distinguished from mononeuropathy, mononeuropathy multiplex (multifocal neuropathy), and disorders of the CNS.
Patients may present with symmetric distal sensory loss, burning, or weakness. Etiologies vary and include medication side effects or manifestations of systemic disease (DM, alcoholism, and HIV). The rate of progression of the polyneuropathy and type (axonal or demyelinating) can help identify its etiology. Polyneuropathy may also be difficult to distinguish from central nervous system disorders such as brain tumor, stroke, or spinal cord lesion.
The etiology of polyneuropathy varies and includes infections, metabolic and immune disorders, neoplasms, postvaccinal effect, and rare genetic disorders such as Charcot-Marie-Tooth.
Initial diagnosis includes obtaining a history of the disease and its progression, physical examination with neurologic testing, and electromyography and nerve conduction studies. Based on EMG studies, a decision can be made as to whether the disorder is axonal or demyelinating. Laboratory tests are recommended by the American Academy of Neurology for each of these categories.
1
Screening for predominantly axonal disorders:
Serum glucose
12
level