Rigors refer to episodes of shaking or exaggerated shivering which can occur with a high fever. It is an extreme reflex response which occurs for a variety of reasons.
Chills is a feeling of coldness occurring during a high fever, but sometimes is also a common symptom which occurs alone in specific people. Severe chills with violent shivering are called rigors.
Both are manifestations of altered temperature regulation – release of cytokines and prostaglandins as part of the inflammatory response, which increases the set point for body temperature in the hypothalamus.
The increased set point causes the body temperature to rise (pyrexia), but also makes the patient feel cold or chills until the new set point is reached.
The purpose of the shivering [rigors] is to produce heat during muscle contraction in a physiological attempt to increase body temperature to the new set point.
Usually chills are seen first, followed by rigors.
Malaria is one of the common reasons for chills and rigors.
Pathophysiology of Rigors
Shivering is a reflex which occurs when someone feels cold. It is done to raise the body temperature.
Hypothalamus in the brain regulates the body temperature and has been likened to internal thermostat. The normal theromstat is set at around 37 degrees. With infection or inflammation, pyrogens, probably cytokines and prostaglandins reset the trigger temperature so that the body feels cold and shaking occurs to raise temperature to the new hypothalamic temperature point.
Other accompanying reflexes that are also body’s attempts to raise temperature are including contraction of erector pilae muscles (‘goose bumps’) and peripheral vasoconstriction.
Different pyrogens can be responsible in different conditions. For example, in malaria it is substance hemozoin which causes chills recurring every 3 to 4 days.
Chills is feeling cold after an exposure to a cold environment. Chills mainly occur at the beginning of the infection and are usually associated with fever.
A chill with shivering or shaking is rigor.
Rigor occurs because the patient’s body is effectively shivering in a physiological attempt to increase the body temperature.
Rigors are a common accompaniment of high fever. They are seen moer in children and are less likely
Causes of Rigors
Rigors are seen in following
- Severe acute respiratory syndrome
- Biliary sepsis
- Visceral abscess
- Urinary tract infections
- Prostate cancer
- Acute cholangitis
- Ulcerative colitis
- Over half of parturients experience shaking rigors. Parturient is a woman about to give birth to the child.
- Septic arthritis
- Rheumatic fever
- Meningococcal infection
- Rat-bite fever
- Lyme disease
- Louse-borne relapsing fever
Drug reactions (usually with intravenous drugs)
- Jarisch-Herxheimer reaction
- Interleukin II
- Anti-TNF-alpha drugs.
- Transfusion reactions
- Generalised pustular psoriasis
- Any severe generalised rash
- After radiotherapy.
- Postoperative infections.
Clinical Presentation and Diagnostic Work Up
The rigor is a symptom that generally presents as shivering associated with chill and often accompanied by fever. It may be described by patients as an attack of uncontrollable shaking.
The history with a suspicion of infection is taken. Symptoms suggestive of respiratory, urinary, biliary disease, and gastrointestinal infections should be searched for.
In children even an otitis media or upper respiratory infection may trigger a rigor.
Enquiry about recent surgical procedures, past history of rheumatic heart disease, recent foreign travels, allergies and recent medication should be done.
Sometimes, the fever and rigors may precede the other symptoms and could present as an early symptom. This is seen in septicemia and pneumonia. Such patients are candidate for observation.
Sometimes it is difficult to find the source and the fever is labeled as pyrexia of unknown origin (PUO)).
The diagnosis is aided by investigations. Following are the general list of investigations, not exhaustive though, and need to be tailored to the patient profile.
- Screening for infection, and basic blood tests:
- CT scan.
- MRI scan.
For acute management temperature lowering drugs or antipyretics are given.. Especially in children, the antipyretic drugs should not routinely be used with the sole aim of reducing the body temperature of a child with fever, only in distress
It is important to find and treat the condition causing the rigors.
For many conditions causing the rigor, hospitalization is necessary, especially in children and in the elderly.
- Tal Y, Even L, Kugelman A, et al. The clinical significance of rigors in febrile children. Eur J Pediatr. 1997 Jun156(6):457-9.
- Suryati BA, Watson M. Staphylococcus aureus bacteraemia in children: a 5-year retrospective review. J Paediatr Child Health. 2002 Jun38(3):290-4.
- Le BH, Rosenthal MA.Prostate cancer presenting with fever and rigors. Intern Med J. 2005 Oct35(10):638.
- Benson MD, Haney E, Dinsmoor M, et al. Shaking rigors in parturients. J Reprod Med. 2008 Sep53(9):685-90.
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