Rigors

Description
A rigor is an episode 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. It should not be ignored, as it is often a marker for significant and sometimes serious infections (most often bacterial). It is important to recognise the patient's description of a rigor, as the episode is unlikely to be witnessed outside hospital, and to be aware of the possible significance of this important symptom.

Pathophysiology1
Shivering is a reflex which occurs when someone feels cold and, physiologically, it serves to raise body temperature. The trigger point at which this reflex occurs is set in the anterior hypothalamus. This has been likened to an internal thermostat.1 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'. The body's attempts to raise temperature are accompanied by other familiar reflex responses including contraction of erector pilae muscles ('goose bumps') and peripheral vasoconstriction. Peripheral vasoconstriction causes cold extremities and pallor. Most of the work done on various pyrogens responsible for mediating this response has been done on animals.1

Epidemiology
Rigors are a common accompaniment of high fever. They occur more commonly in children.2 They are less likely to occur in the elderly.3 However, they are a predictor of bacteraemia and bacterial infection in young and old.2,3 History: o The sudden attack of severe shivering accompanied by a feeling of coldness ('the chills') is called a rigor and is associated often with a marked rise in body temperature. It may be described by patients as an attack of uncontrollable shaking. o A history of rigors should raise suspicion of infection, particularly bacterial infection. Enquiry should be made about: Symptoms suggestive of local infection, particularly respiratory infections, urinary infections, biliary disease, and gastrointestinal (GI) infections. Recent surgical procedures. Any relevant past medical history such as rheumatic heart disease. Recent foreign travel. Medication and allergies. Examination: o This should be performed according to the history. o Care should be taken in children where even an otitis media or upper respiratory infectionmay have triggered a rigor. o It should be remembered that rigors can be an early symptom in septicaemia, particularlymeningococcal septicaemia.4 Appropriate care should be taken to examine for rashes as well as signs of meningism, especially in children. o A history of rigors in the night may be followed by signs of a pneumonia the next day.

Presentation

Differential diagnosis
The classic differential diagnosis for rigors includes: Biliary sepsis (part of Charcot's triad)5 Pyelonephritis Visceral abscess (including lung, liver and paracolic) Malaria

It is important in children to differentiate a rigor from a febrile convulsion. In adults care should be taken to differentiate from a fit or convulsion. A review of the recent literature demonstrates the range of conditions associated with rigors. These may be: Cardiac: o Infective endocarditis o Pericarditis o Lemierre's syndrome6,7 o Dressler's syndrome8 Pulmonary: o Pneumonia9,10,11 o Severe acute respiratory syndrome (SARS)12,13 Genitourinary: o Urinary tract infections o Pyelonephritis o Prostatitis o Prostate cancer14 Obstetric:15 o Over half of parturients experience shaking rigors o Epidurals and fever seem to be associated with the rigors Rheumatological: o Septic arthritis16 o Rheumatic fever Infectious diseases: o Meningococcal septicaemia 4 o Malaria17 o Rat bite fever18 o Filariasis19 o Brucellosis20,21,22 o Tuberculosis (miliary)23,24,25 o Lyme disease26 o Louse-borne relapsing fever (endemic in Ethiopia)27 GI: o Gastroenteritis o Acute cholangitis5 o Ulcerative colitis28 Drug reactions (usually intravenous)29,30: o Jarisch-Herxheimer reaction29,31 o Gentamicin o Vancomycin o Interleukin II o Amphotericin B o Anti-TNF alpha drugs Transfusion reactions: o 30% of transfusion reactions are associated with rigors 32 o Many types of blood product transfusions Dermatological: o Generalised pustular psoriasis33 o Any severe generalised rash, especially in children Iatrogenic: o Haemodialysis34 o After radiotherapy35 o After bone marrow transplant o Catheterisation3,36 o Postoperative infections

Investigations

This will depend on the clinical assessment and likely cause. Very often history and examination will reveal a source of infection, and treatment can be commenced without extensive investigation. However, in children, extreme care should be taken and hospital admission will usually be indicated particularly when the child remains febrile and no source of infection is found (the pyrexia of unknown origin (PUO)). The following list is not exhaustive. In particular, an ill child investigation is likely to include: Screening for infection, and basic blood tests: o Full blood count, urea and electrolytes, erythrocyte sedimentation rate, C-reactive protein, and liver function tests o Blood cultures o Urine for microscopy and culture o Lumbar puncture and cerebrospinal fluid analysis Imaging: o Chest X-ray o CT scan o MRI scan

Management
Temperature-lowering measures, particularly in children, are important. It is important to find and treat the source of infection. It is likely that hospitalisation will be required for diagnosis and treatment if the patient remains unwell and febrile. Admission to hospital is more likely to be required in children and in the elderly.