Understanding Rigors

April 3rd, 2025

Rigors can be distressing for patients and may signal serious medical conditions requiring prompt evaluation and management. This article explores pathophysiology, causes, differential diagnosis, evaluation, and treatment of rigors, with a focus on evidence-based approaches.

Pathophysiology of rigors

Rigors occur due to the body's thermoregulatory response to pyrogens, which trigger an increase in the hypothalamic set-point temperature. This process involves:

• Cytokine release: Infection or inflammation stimulates immune cells to release pyrogens such as interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-α), and prostaglandins.

• Hypothalamic response: Pyrogens act on the hypothalamus to raise the body's temperature set-point.

• Muscle contraction: In an effort to reach the new set-point, the body induces muscle contractions (shivering) to generate heat.

• Peripheral vasoconstriction: To minimize heat loss, blood vessels constrict, leading to cold sensations and chills.

Common causes of rigors

Rigors are typically associated with infections but can also result from non-infectious conditions. Below are the major causes:

1. Infectious causes

Infections that cause bacteremia or systemic inflammation are the most common triggers of rigors. These include:

Bacterial infections

• Sepsis (Gram-negative and Gram-positive bacteremia)

• Pneumonia (Streptococcus pneumoniae, Legionella)

• Urinary tract infections (Pyelonephritis, urosepsis)

• Endocarditis (Staphylococcus aureus, Streptococcus species)

• Meningitis (Neisseria meningitidis, Streptococcus pneumoniae)

• Cellulitis with bacteremia

Viral infections

• Influenza

• COVID-19

• Dengue fever

• Malaria (Plasmodium species, notably P. falciparum)

Parasitic and fungal infections

• Malaria

• Histoplasmosis

• Cryptococcosis

• Candidemia

2. Non-infectious causes

Though less common, rigors can be triggered by non-infectious conditions, including:

Autoimmune and inflammatory diseases

• Systemic lupus erythematosus (SLE)

• Still's disease (Adult-onset)

• Rheumatoid arthritis with systemic involvement

Malignancies

• Leukemia and lymphoma

• Tumor lysis syndrome

• Paraneoplastic syndromes

Drug reactions

• Amphotericin B

• Vancomycin ("Red Man Syndrome")

• Chemotherapeutic agents

• Post-transfusion reactions

Other conditions

• Post-surgical systemic inflammatory response

• Hypoglycemia

• Thyroid storm

Differential diagnosis

Distinguishing rigors from other conditions that cause shivering, tremors, or chills is crucial for accurate diagnosis. Consider the following:

• Seizures: Sudden onset, altered mental status, tonic-clonic movements

• Tremors: Rhythmic and voluntary movements, no fever

• Hypothermia: Shivering due to cold exposure, low core body temperature

• Drug withdrawal: Opioid or alcohol withdrawal with tremors and autonomic instability

• Neuroleptic malignant syndrome (NMS): Hyperthermia, autonomic instability, rigidity

Clinical evaluation

A systematic approach to evaluating a patient with rigors includes:

1. History

• Onset and duration: Sudden or gradual, recurrent episodes

• Associated symptoms: Fever, chills, dyspnea, cough, dysuria, rash

• Recent exposures: Travel history, hospitalizations, animal contact, tick bites

• Comorbidities: Immunosuppression, malignancy, autoimmune disease

• Medications: Recent antibiotics, chemotherapy, transfusions

2. Physical examination

• Vital signs: Fever, tachycardia, hypotension, oxygen saturation

• Skin findings: Rash, cellulitis, petechiae

• Neurological status: Altered mental status, nuchal rigidity

• Pulmonary exam: Crackles, wheezing, respiratory distress

• Abdominal and genitourinary exam: Costovertebral angle tenderness, hepatosplenomegaly

3. Diagnostic workup

The workup should be guided by clinical suspicion:

Blood tests

• Complete blood count (CBC) with differential

• Blood cultures (Two sets, from different sites)

• Inflammatory markers (C-reactive protein [CRP], procalcitonin)

• Liver and renal function tests

• Lactate levels (for sepsis assessment)

Microbiological tests

• Urinalysis and urine culture

• Sputum Gram stain and culture

• Cerebrospinal fluid (CSF) analysis if meningitis is suspected

Imaging

• Chest X-ray (pneumonia, tuberculosis)

• CT abdomen/pelvis (abscess, pyelonephritis)

• Echocardiography (endocarditis workup)

Prognosis and complications

The prognosis of rigors depends on the underlying cause. Prompt identification and treatment reduce morbidity and mortality, particularly in sepsis. Possible complications include:

• Septic shock, requiring intensive care and vasopressors

• Multi-organ failure, which can affect the kidneys, liver, lungs, and heart

• Disseminated intravascular coagulation (DIC), leading to widespread clotting and bleeding

• Chronic recurrent infections, such as endocarditis or tuberculosis, requiring prolonged antimicrobial therapy

Rigors are a significant clinical symptom that warrants thorough evaluation to determine the underlying etiology. A systematic approach — including history, physical examination, diagnostic testing, and timely management — ensures optimal patient outcomes. Identifying the cause of rigors promptly can prevent serious complications and improve prognostic outcomes, particularly in infectious diseases.