This post is co-written with the guest writer Ahmed Abdul Azim, MD.

Not all fevers are caused by infections.

It is important that every patient presenting with fever is evaluated for an infection….. but what do you do when no infection is found?

Why are non-infectious causes of fever important to know?

If a patient is treated for a presumed infectious fever when they don’t have an infection:

• there is a delay in identifying the correct diagnosis
• they are exposed to prolonged courses of unnecessary antibiotics

 

Definition of fever

Fever = 38.3°C (101°F) or above¹

Pyrogenic agents = substances that can induce a fever.
a) Exogenous pyrogens – external substances that activate our immune system to induce a fever (ex. microbial toxins)
b) Endogenous pyrogens – cytokines that induce fever in our body
(ex. IL-1, IL-6, tumor necrosis factor, IFN-α, ciliary neutrotrophic factor, and likely others)

 

Non-infectious causes of fever:

1. Rheumatologic/autoimmune – activation of immune system that stimulates the production of pyrogenic cytokines
– the cause of ~30% of fevers of unknown origin

a) Adult-onset Still’s disease – younger patients, daily fevers >39°C, rash, arthritis
b) Giant cell arteritis – older patients, vision changes, jaw claudication
c) Others – polyarteritis nodosa, Takayasu’s arteritis, granulomatosis with polyangiitis, etc.

2. Malignancy – tumor cells release pyrogenic cytokines

a) Lymphomas and leukemias – most common; seen in high burden of disease
b) Myelodysplastic syndromes
c) Renal cell carcinoma – ~20% of cases present with fevers
d) Hepatocellular carcinoma or liver metastases
e) Atrial myxomas

3. Drug-induced fever – 3-5% of drug-related adverse reaction in hospitalized patients include fevers⁶
– typically occurs 7-10 days after drug initiation, but can be as soon as 24 hours and as far away as a few years from drug initiation⁷
– patients typically appear “inappropriately” well
– eosinophilia (>500/mm3) occurs in 20-25% of patients with drug-induced fevers¹⁰
– PATHOPHYSIOLOGY:

a) Hypersensitivity reaction – due to activation of T cell immune response by drug, its metabolite, or the formation of an immune complex
– typically occurs ~3-10 days after drug exposure
– typically resolves 72-96 hours after discontinuation of drug (but can be more delayed)
– symptoms will recur immediately upon rechallenge

1) Antimicrobials – most common cause of drug fever
– minocycline, beta-lactams (penicillin-based > cephalosporins¹⁰), sulfonamides, nitrofurantoin
2) Anticonvulsants – carbamazepine, phenytoin, phenobarbital
3) Allopurinol
4) Others

– DRESS syndrome – a severe type of drug hypersensitivity reaction
(typically occurs 2-6 weeks after drug exposure)

b) Administration-related – typically last <48 hours

1) Vaccines – stimulation of the immune system → release of pyrogenic cytokines
2) Amphotericin B – exogenous pyrogenic agents

c) Pharmacologic action of the drug – transient fever; self-resolving

1) Anti-neoplastic agents – cause severe and rapid tumor cell lysis → release of endogenous pyrogenic agents → inflammatory response (fever)
2) Antimicrobials – cause rapid death of microbes → microbial cell lysis → release of exogenous pyrogenic substances → inflammatory response (fever)
–  ex. Jarisch-Herxeimer reaction in syphilis treatment with penicillin

d) Altered thermoregulation – disturbance of the central hypothalamic thermoregulation function and/or increased heat production

1) Exogenous thyroid hormone
2) Anticholinergic drugs
3) Sympathomimetic agents

e) Idiosyncratic drug reactions

1) Serotonin syndromes – linezolid, SSRIs
2) Neuroleptic malignant syndrome
– anti-psychotics, dopamine antagonists
3) Malignant hyperthermia syndrome
– inhaled anaesthetics, paralytic agents
4) G-6-PD deficiency – dapsone, primaquine, nitrofurantoin, etc.

4. Other causes

1) Transfusion of blood cells – RBCs, platelets, WBCs
2) Central fevers – fevers due to central thermodysregulation due to CNS damage
– more common with CNS hemorrhage and brain tumors¹¹
– fever onset within 72 hours of sustaining CNS hemorrhage
3) Thromboembolism – typically <102°F
4) Endocrine – thyroid storm; adrenal insufficiency
5) Pulmonary – ARDS, aspiration pneumonitis, cryptogenic organizing pneumonia
6) Intra-abdominal – acute pancreatitis, cholecystitis, mesenteric ischemia

*Non-infectious causes of fevers are diagnoses of exclusion. A patient MUST have an appropriate workup for infectious causes prior to considering any of the non-infectious causes of fever.

*A lot of these diagnoses need to be made based on clinical symptoms and signs and requires a high degree of suspicion.

*Fever is a sign of an underlying inflammatory process.
DO NOT TREAT THE FEVER — TREAT THE UNDERLYING CAUSE.

 

References:

1. O’Grady NP, Barie PS, Bartlett JG, et al. Guidelines for evaluation of new fever in critically ill adult patients: 2008 update from the American College of Critical Care Medicine and the Infectious Diseases Society of America. Crit Care Med. 2008; 36(4):1330-1349.
2. Dekker AR, Verheij TJ, and van der Velden AW. Inappropriate Antibiotic Prescription for Respiratory Tract Indications: Most Prominent in Adult Patients. Family Practice. 2015; 32(4):401-407.
3. Mackowiak PA, Wasserman SS, and Levine MM. A Critical Appraisal of 98.6°F, the Upper Limit of the Normal Body Temperature, and Other Legacies of Carl Reinhold August Wunderlich. JAMA. 1992; 268(12):1578-1580.
4. Obermeyer Z, Samra JK, and Mullainathan S. Individual Differences in Normal Body Temperature: Longitudinal Big Data Analysis of Patient Records. BMJ. 2017; 359:j5468.
5. Westbrook A, Pettila V, Nichol A, et al. Transfusion Practice and Guidelines in Australian and New Zealand Intensive Care Units. Intensive Care Med. 2010; 36(7):1138-1146.
6. Lipsky, BA and Hirschmann JV. Drug Fever. JAMA. 1981; 245(8):851-854.
7. Mackowiak, PA. Southwestern Internal Medicine Conference: Drug Fever: Mechanisms, Maxims and Misconceptions. Am J Med Sci. 1987; 294(4):275-286.
8. Patel, RA and Gallagher JC. Drug fever. Pharmacotherapy. 2010; 30(1):57-69.
9. Johnson DH and Cunha BA. Drug fever. Infect Dis Clin North Am. 1996; 10(1):85-91.
10. Oizumi K, Onuma K, Watanabe A, et al. Clinical Study of Drug Fever Induced by Parenteral Administration of Antibiotics. Tohoku J Exp Med. 1989; 159(1): 45-56.
11. Hocker SE, Tian L, Li G, et al. Indicators of Central Fever in the Neurologic Intensive Care Unit. JAMA Neurology. 2013; 70(12):1499-1504.
12. Porat R and Dinarello CA. Pathophysiology and treatment of fever in adults. In Baron EL, ed. UpToDate. Waltham, Mass.: UpToDate, 2018. [https://www.uptodate.com/contents/pathophysiology-and-treatment-of-fever-in-adults]. Accessed Dec 26, 2018.