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  1. The differential diagnosis includes meningitis or encephalitis, neuroleptic malignant syndrome, serotonin syndrome, heat exhaustion, anticholinergic drug use, and toxin exposure.

  2. Neuroleptic malignant syndrome

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Temp Heart Rate Blood Pressure Mental Status Rigidity Tremor Clonus
NMS >38°C Tachycardia Hypertensive or labile Agitated, delirium, confusion, catatonia Yes Yes No
Serotonin Syndrome >38°C Tachycardia Hypertension may progress to shock From mild agitation to agitated delirium Yes Yes Yes

CLINICAL PEARL. Serotonin Syndrome will cause inducible clonus and ocular clonus; neuroleptic malignant syndrome does not cause clonus.


  1. You should anticipate hyperpnea (Kussmaul breathing). This is deep regular respiration, it occurs in response to the metabolic acidosis. It increases alveolar ventilation creating a respiratory alkalosis by increased CO2 excretion to compensate for the metabolic acidosis.

  2. Kussmaul breathing is seen with any severe metabolic acidosis and it is a direct effect of salicylate toxicity. It may also be seen with decreased tissue oxygen delivery from severe anemia or hemorrhage.

  3. The Cheyne–Stokes respiratory pattern is cyclic hyperventilation followed by compensatory apnea.

  4. The periodic Cheyne–Stokes breathing is caused by a phase delay in the feedback controls attempting to maintain a constant PaCO2. This is the most common periodic breathing pattern. In each cycle, the rate and amplitude of successive breaths increase to a maximum, then progressively diminish into the next apneic period. Pallor may accompany the apnea. The patient is frequently unaware of the irregular breathing. Patients may be somnolent during the apneic periods and then arouse and become restless during the hyperventilation phase.

  5. It may be seen during sleep in normal children and the aged. Other causes are disorders of the cerebral circulation (stroke, atherosclerosis), heart failure and low cardiac output of any cause, increased intracranial pressure (meningitis, hydrocephalus, brain tumor, subarachnoid hemorrhage, intracerebral hemorrhage), head injury, drugs (opiates, barbiturates, alcohol), and at high altitude during sleep before acclimatization.

CLINICAL PEARL. Irregular breathing—Biot breathing. This is an uncommon variant of Cheyne–Stokes respiration in which periods of apnea alternate irregularly with a series of breaths of equal depth that terminate abruptly. It is most often seen in meningitis.


  1. The blood pressure drops without a corresponding increase in pulse. This indicates autonomic insufficiency.

  2. Causes include decreased intravascular volume (hemorrhage, dehydration), loss of vascular tone (autonomic insufficiency-multisystem atrophy), deconditioning after a prolonged illness, peripheral neuropathies (diabetes, tabes dorsalis, alcoholism), medications (tricyclic antidepressants, vasodilators, ganglion blockers), and impaired venous return (ascites, pregnancy, venous insufficiency, inferior vena cava obstruction or hemangiomas of the legs).

  3. Multiple system atrophy.

  4. Parkinsonism type: patients have slow movement, rigidity, and tremor. Cerebellar type: patients have difficulties with coordination and speech. Combined type: patients will have Parkinsonism and cerebellar dysfunction.

CLINICAL PEARL. When the drop in BP is not accompanied by a ...

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