CONVULSIONS

To formulate a differential diagnosis of convulsions, one must use both physiology and anatomy. The anatomic causes are charted in Table 19.

CONVULSIONS

CONVULSIONS

Irritability of the nerve cell is caused by the same physiologic factors that lead to irritability of a muscle cell: anoxia, hypoglycemia, and electrolyte imbalances. Any condition causing anoxia may cause a seizure; thus, focal arterial spasm (e.g., TIA) may lead to seizures. Obstruction of the artery by emboli, thrombi, or atheromatous plaques may cause focal anoxia and seizures, whereas diffuse cerebral anoxia is more likely to cause syncope and coma. Acute blood loss (anemic anoxia) or acute reduction in cardiac output (as in Stokes–Adams disease and various arrhythmias) are infrequent causes of seizures. Aortic stenosis and insufficiency may occasionally cause seizures by relative reduction in cardiac output compared to demand (as during exercise).

Hypoglycemia is more likely to cause a coma than a seizure. Anything that reduces the blood sugar severely (< 40 mg/dL), such as exogenous insulin overdose, islet cell adenoma, Addison disease, and hypopituitarism, may cause a seizure.

Irritability of the nerve cell is more often caused by electrolyte alterations. The same equations that applied to muscle applies here: Neuronal irritability × Na+, K+, pH⁄Ca++, Mg++, H+ Hypocalcemia may at first lead to tetany, simulating a convulsion. The causes of hypocalcemia include hypoparathyroidism, vitamin D deficiency, malabsorption syndrome, calcium-losing nephropathy, and chronic nephritis. Ionizable calcium is decreased by alkalosis, respiratory or metabolic. Hypomagnesemia must be ruled out, especially in chronic alcoholics and malabsorption syndromes. Water intoxication should be considered in inappropriate antidiuretic hormone (ADH) syndrome (relative dilution of both calcium and magnesium).

Moving from the physiologic causes of seizures to the anatomic analysis, the physician’s main consideration is that something mechanical is irritating the nerve cell. The nerve cell may be irritated by a tumor of the supporting tissue, an abscess or a hematoma. Pressure from inflammatory lesions in the meninges (i.e., meningitis or epidural abscess) or hemorrhage into this layer (subdural or epidural hematoma and subarachnoid hemorrhages) may be the mechanical irritant. Focal accumulation of fluid in the brain substance as in encephalitis, concussions, and increased intracranial pressure from whatever causes may lead to a seizure. A depressed skull fracture is occasionally the mechanical irritant, as is a scar from an old skull injury. Infiltration of the brain by metals such as lead and copper (i.e., Wilson disease) are worth considering in children, particularly infiltration of the brain by a foreign cell (i.e., leukemia). Reticuloendotheliosis and mucopolysaccharidosis should be considered. Turning to exogenous factors, one must consider a host of chemicals and drugs that may cause seizures, most commonly alcohol, paint thinners, lidocaine (Xylocaine), phenothiazine drugs, and bromides. A bolus of almost any substance may occasionally cause seizures if it is large enough.

Occasionally, degenerative and demyelinating disease may present with seizures. On the other hand, lupus erythematosus and other collagen diseases may frequently present with seizures. Finally, one should not forget idiopathic epilepsy.

Approach to the Diagnosis

The first thing to do is ascertain whether the motor disturbance or episode of loss of consciousness was really a seizure. Hysterical seizures are not associated with incontinence or tongue biting. There is often an aura with real seizures but not so with hysterical seizures.

Next, a careful history from the immediate family or friend is important. Be sure to ask about previous head trauma (including birth trauma), anoxia, meningitis, or encephalitis. Inquiry into drug or alcohol abuse is essential.

A thorough neurologic examination is a must. If the clinician is too busy or not equipped to do this, referral to a neurologist is done at this point. If there are focal neurologic signs or papilledema, there is a strong chance the patient has a space-occupying lesion such as tumor, subdural hematoma, or abscess and will need a neurologist anyway.

The clinical picture will help determine the cause of the seizures. If there is alcohol or drug use, toxic encephalopathy is suspected. If there is fever, meningitis or encephalitis must be considered in the differential. If there is a heart murmur or irregular heart beat, cerebral embolism should be suspected. A history of trauma suggests posttraumatic epilepsy. A history of optic neuritis makes one suspicious of multiple sclerosis. A history of high-risk sexual behavior suggests AIDS may be the cause. A history of cancer makes it important to rule out cerebral metastasis.

The initial workup should include a CBC, urinalysis, sedimentation rate, ANA, VDRL test, chemistry panel, drug screen, wake-and-sleep EEG, and skull x-ray. Patients with suspected grand mal epilepsy or focal motor seizures need either a CT scan or MRI to rule out a space-occupying lesion. This is true of all patients with complex partial seizures as well.

Patients suspected of having meningitis or encephalitis need a spinal tap. Patients with possible cerebral embolism need an ECG, echocardiogram, blood cultures, and a cardiology consult. If AIDS is suspected, an HIV antibody titer is ordered. Patients with possible multiple sclerosis need a spinal fluid analysis, and visual, somatosensory or brain stem evoked potential studies. Elderly patients should have a chest x-ray to exclude a primary tumor of the lung.

Other Useful Tests

1. Holter monitoring (heart block)
2. Ambulatory EEG monitoring (epilepsy with infrequent seizures)
3. Seventy-two–hour fast (hypoglycemia)
4. 24-hour urine calcium (hypoparathyroidism)
5. Stool for ova and parasites (cysticercosis)
6. Urine porphobilinogen (porphyria)
7. Blood lead level (lead encephalopathy).

Book Source Details

• Book Title: Differential Diagnosis in Primary Care
• Author(s): R. Douglas Collins
• Year of Publication: 2007
• Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2007 Lippincott Williams & Wilkins.

Other Book Chapters Related to Convulsions

Read excerpts from these other book chapters related to Convulsions:

Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2008 Williams & Wilkins.

More About Causes of Convulsions

• Back to symptom: Convulsions: Introduction (review 559 causes)
• Next Book Extract About Convulsions: Seizures, absence (Handbook of Signs & Symptoms (Third Edition))
• All Book Extracts: All Online Book Extracts for Convulsions

More About This Book: Title: Differential Diagnosis in Primary Care Authors: R. Douglas Collins Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 0-7817-6812-8

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