CONVULSIONS
To formulate a differential diagnosis of convulsions, one must use both
physiology and anatomy.The anatomic causes are charted in Table
19.
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., transient ischemic attack [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)
and 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
severely reduces the blood sugar (<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 equation that applied to muscle applies here:
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 in 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. In contrast, 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
that 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 that acquired immunodeficiency syndrome
(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, a human
immunodeficiency virus (HIV) antibody titer is ordered. Patients with
possible multiple sclerosis need a spinal fluid analysis, and visual,
somatosensory, or brainstem-evoked potential studies. Elderly patients
should have a chest x-ray to exclude a primary tumor of the lung.
Other Useful Tests
-
Holter monitoring (heart block)
-
Ambulatory EEG monitoring (epilepsy with infrequent seizures)
-
72-hour fast (hypoglycemia)
-
24-hour urine calcium (hypoparathyroidism)
-
Stool for ova and parasites (cysticercosis)
-
Urine porphobilinogen (porphyria)
-
Blood lead level (lead encephalopathy).
Pictures
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Book Source Details
- Book Title: Differential Diagnosis in Primary Care
- Author(s): R. Douglas Collins MD, FACP
- 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:
Medical Books Excerpts
- Seizures
- "A Pocket Manual of Differential Diagnosis" (1999)
- [ read ]
- Seizures
- "The 10-Minute Diagnosis Manual: Symptoms and Signs in the Time-Limited Encounter" (2000)
- [ read ]
- Seizures
- "The Diagnostic Approach to Symptoms and Signs in Pediatrics" (2006)
- [ read ]
Copyright Details: Differential Diagnosis in Primary Care, Copyright © 2008 Williams & Wilkins.
More About Causes of Convulsions
» Next page: Medications causing Convulsions
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