Disorders with Rigidity

Disorders with Rigidity is a topic covered in the Washington Manual of Medical Therapeutics.

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General Principles

  • NMS is associated with the use of neuroleptic drugs, certain antiemetic drugs (e.g., metoclopramide, promethazine), and sudden withdrawal of dopamine agonists (L-dopa in PD) and can even occur as an “off” phenomenon in PD patients experiencing severe “on–off” fluctuations.
    • Features include hyperthermia, altered mental status, muscular rigidity, and dysautonomia.
    • Laboratory abnormalities include a leukocytosis and a markedly elevated creatine kinase with myoglobinuria.
    • Treatment includes discontinuing precipitating drug(s), restarting medications that were stopped (in the case of a PD patient), cooling and paralytics (if necessary), monitoring and supporting vital functions (arrhythmias, shock, hyperkalemia, acidosis, renal failure, and management of rhabdomyolysis), and administering dantrolene and/or bromocriptine. Treatment is essentially identical to that used for malignant hyperthermia (see the following text).
  • Serotonin syndrome results from excessive serotonergic activity, especially following recent dosage changes of SSRIs, MAOIs, and TCAs.
    • It presents as a triad of mental status change, autonomic overactivity, and neuromuscular abnormalities. Distinguishing features of serotonin syndrome from NMS include the degree of mental status change, seizures, and the marked hyperreflexia. However, in certain circumstances, the two can be difficult to distinguish from one another.
    • Hyperthermia, tremor, nausea, vomiting, and clonus are common signs.
    • Treatment includes removal of offending drugs, aggressive supportive care, cyproheptadine, and benzodiazepines.1
  • Malignant hyperthermia is the acute development of high fever, obtundation, and muscular rigidity following triggering factors (e.g., halothane anesthesia, succinylcholine).
    • The most common etiology is an autosomal dominant mutation in the ryanodine receptor (RYR1), making a screen of the family history a critical part of the preoperative evaluation. Abnormalities in this calcium channel predispose patients to an elevation in intracytoplasmic calcium triggered by certain anesthetics. Other ion channels have also been identified, and children with dystrophinopathies and other forms of muscular dystrophy are also at an increased risk.
    • Serum creatine kinase is markedly elevated. Renal failure from myoglobinuria and cardiac arrhythmias from electrolyte imbalance can be life threatening.
    • Successful management requires prompt recognition of early indicators of the syndrome (increased end-tidal carbon dioxide, tachycardia, acidosis, and/or muscle rigidity; note, hyperthermia comes later if at all); discontinuation of the offending anesthetic agent; aggressive supportive care that focuses on oxygenation/ventilation, circulation, correction of acid–base and electrolyte derangements; and administration of dantrolene sodium, 1–10 mg/kg/d, for at least 48–96 hours to reduce muscular rigidity.
  • Tetanus typically presents with generalized muscle spasm (especially trismus) caused by the exotoxin (tetanospasmin) from Clostridium tetani, a Gram-positive bacillus commonly found in intestinal flora and soil.
    • The organism usually enters the body through wounds. Onset typically occurs within 7–21 days of an injury.2
    • Patients who are unvaccinated or have reduced immunity are at risk, underscoring the importance of prevention by tetanus toxoid boosters following wounds. Tetanus may occur in drug abusers who inject SC.
    • Management consists of supportive care, particularly airway control (laryngospasm) and treatment of muscle spasms (benzodiazepines, barbiturates, analgesics, and sometimes neuromuscular blockade). Cardiac arrhythmias and fluctuations in BP can occur. Recovery takes months. Shorter incubation periods (≤7 days) portend more severe courses and a worse prognosis.
    • The patient should be kept in quiet isolation, sedated but arousable.
    • Specific measures include wound debridement, penicillin G or metronidazole, and human tetanus immunoglobulin (3000–6000 units IM).
    • Active immunization is needed after recovery (total of three doses of tetanus and diphtheria toxoid spaced at least 2 weeks apart).

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