The Entangled Erythrocyte: Disentangling High ESR States in the Patient with Inflammatory Arthritis

An Authoritative Clinical Review for the Practicing Internist

 Dr Neeraj Manikath

 

 

1. A Compelling Clinical Introduction: The Siren Song of the Sed Rate

Mrs. Eleanor V., a 58-year-old woman with a 12-year history of seropositive rheumatoid arthritis (RA), presents to the emergency department with profound fatigue, a 5-kilogram weight loss over six weeks, and generalized myalgias. Her RA has been historically managed with methotrexate and adalimumab, achieving low disease activity for the past four years. Her primary care physician, alarmed by her constitutional symptoms, ordered a blood panel. Her hemoglobin is 9.8 g/dL (baseline 12.5 g/dL), and her ESR is reported as a staggering 118 mm/hr. Her CRP, however, is 6 mg/L (normal < 5).

 

The admitting team, anchoring on the astronomically high ESR and the history of inflammatory arthritis, diagnoses her with an acute rheumatoid flare. They administer a pulse of intravenous methylprednisolone. Over the next 48 hours, her fatigue worsens, she becomes delirious, and her creatinine triples.

 

The team had fallen victim to diagnostic anchoring. Mrs. V. did not have an RA flare; she had occult Giant Cell Arteritis (GCA) with overlapping Polymyalgia Rheumatica (PMR), complicated by an evolving multiple myeloma—a condition for which her long-standing RA was an independent risk factor. The high-dose steroids precipitated a crisis in her undiagnosed paraproteinemia-induced kidney disease.

 

Inflammatory arthritis is a smoldering fire. When a patient with known RA, Psoriatic Arthritis (PsA), or Ankylosing Spondylitis (AS) walks through your door with an ESR of 100, the easiest conclusion is that their fire has flared. However, as a master clinician, you must ask yourself: Is this the old fire burning hotter, or is a new fire lit in the same forest?

 

Epidemiologically, patients with RA have a 1.5- to 2-fold increased risk of lymphoproliferative malignancies, a 2- to 3-fold increased risk of GCA/PMR, and a substantially elevated risk of secondary amyloidosis and occult infections due to immunosuppression. When faced with an extreme ESR elevation in this population, the default must not be "flare." The default must be "entanglement." This review will equip you with the clinical heuristics, pathophysiological frameworks, and state-of-the-art diagnostic algorithms to disentangle the confounders of a high ESR in the inflammatory arthritis patient.

 

Clinical Takeaway: An ESR > 100 mm/hr in a patient with historically well-controlled inflammatory arthritis is rarely just an arthritis flare. It is a diagnostic siren demanding a comprehensive search for infection, malignancy, or a secondary inflammatory state.

 

 

 

2. Pathophysiology: The Physics and Biology of the Sed Rate (Only What is Actionable)

To understand why ESR is such a tangled biomarker, you must understand its physics. The ESR measures the distance red blood cells (RBCs) fall in a vertical tube of anticoagulated blood over one hour.

 

The settling of RBCs is governed by two opposing forces: gravity pulling the cells down, and plasma viscosity and RBC surface charge (zeta potential) pushing them apart. Normally, RBCs repel each other and fall slowly. However, when acute-phase reactants—specifically fibrinogen, immunoglobulins (polyclonal and monoclonal), and alpha-2 macroglobulin—increase, they neutralize the negative surface charge of the RBCs (sialic acid residues). This causes the RBCs to stick together in stacks, known as rouleaux formation.

 

Rouleaux acts like a snowball rolling down a hill: the aggregated mass has a smaller surface-area-to-volume ratio than individual cells, reducing plasma drag, causing them to settle much faster.

 

Why is this clinically actionable?
Because ESR is a lagging indicator driven heavily by immunoglobulins and fibrinogen, it is decoupled from acute, purely cytokine-driven inflammation (which CRP tracks more faithfully).

 

1. Immunoglobulins (IgG, IgA, IgM): Any condition that spikes immunoglobulins—whether polyclonal (chronic infections, HIV, Hepatitis C, Sjögren’s) or monoclonal (multiple myeloma, MGUS, Waldenström’s)—will spike the ESR, sometimes independent of true tissue inflammation.

2. RBC Morphology: The physics of rouleaux requires normal RBC shape. In sickle cell disease, spherocytosis, or severe poikilocytosis, the ESR will be artificially low, even in the presence of sepsis. Conversely, anemia reduces the hematocrit, decreasing plasma drag and falsely elevating the ESR.

3. The Fibrinogen Lag: Fibrinogen has a half-life of roughly 100 hours. Therefore, an acute surgical insult or infection will spike ESR days after the event, and the ESR will remain elevated long after the patient has clinically recovered.

 

Clinical Takeaway: ESR reflects the physics of blood (RBCs, immunoglobulins, fibrinogen), whereas CRP reflects the biology of acute cytokine-driven inflammation (IL-6 driven hepatic synthesis). When they disagree, look at the patient's hematologic and protein profile.

 

 

 

3. The "TANGLED" Mnemonic: A Framework for the Differential

When evaluating a high ESR in the inflammatory arthritis patient, use the TANGLED framework to systematically categorize the potential entanglements:

 

● T – Treatment artifacts and Toxicities (Biologics, IVIG, Drug-induced lupus)

● A – Amyloidosis (AA secondary to chronic RA)

● N – Neoplasia (Lymphoma, Multiple Myeloma, solid tumors)

● G – Giant Cell Arteritis / Polymyalgia Rheumatica (Overlap syndromes)

● L – Liver failure and Low albumin (Nephrotic syndrome, severe malnutrition)

● E – Erythrocyte artifacts (Anemia, macrocytosis, technical errors)

● D – Deep infections (Occult abscesses, Osteomyelitis, Endocarditis)

 

Let us dissect the most clinically treacherous of these entanglements.

 

 

 

4. The Neoplastic Trap (N)

4.1. Lymphoproliferative Disease

Patients with RA have a 1.5- to 2-fold increased risk of Non-Hodgkin Lymphoma (NHL), particularly Diffuse Large B-Cell Lymphoma (DLBCL), driven by chronic B-cell activation, immune dysregulation, and certain therapies.

 

Diagnostic Nuances:
The challenge is that lymphoma and an RA flare share identical constitutional symptoms: fatigue, night sweats, weight loss, and arthralgias. Furthermore, a paraproteinemia (often seen in MGUS or smoldering myeloma) can cause a wildly elevated ESR while the CRP remains perfectly normal.

 

● The CRP/ESR Discordance: If you see an ESR of 110 and a CRP of 4, your differential must narrow toward a paraprotein. The excess monoclonal immunoglobulins drive rouleaux, but without a massive IL-6 cytokine storm, the CRP isn't triggered.

● Actionable Step: In any RA patient with a disproportionate ESR, order a Serum Protein Electrophoresis (SPEP) and Serum Free Light Chains (SFLC). If there is an M-spike, the ESR elevation is a physics artifact of monoclonal proteins, not a reflection of arthritis activity.

 

4.2. Solid Tumors and Renal Cell Carcinoma

Never underestimate the paraneoplastic potential of solid tumors. Renal Cell Carcinoma (RCC) is notorious for secreting IL-6, causing a massive systemic inflammatory response. A patient with RA who presents with an ESR of 100, new-onset anemia, and left varicocele or flank pain needs a CT abdomen/pelvis, not a joint injection.

 

 

 

5. The Giant Cell Arteritis Overlap (G)

One of the most frequent and dangerous entanglements in the RA patient over the age of 50 is the onset of Giant Cell Arteritis (GCA). The prevalence of GCA is significantly increased in patients with established RA.

 

5.1. The Diagnostic Pitfall

When a 68-year-old woman with RA presents with profound shoulder and hip stiffness, it is exceptionally easy to label it an RA flare. But if her ESR is > 80 and she mentions a new, transient headache, or simply that her jaw aches after chewing a steak (jaw claudication), you are dealing with GCA until proven otherwise.

 

Diagnostic Nuances:

● Temporal Artery Exam: The master clinician does not simply palpate the temporal artery; they roll the fingers gently to assess for thickness, nodularity, and tenderness. A normal pulse does not rule out GCA, but an easily palpable, thickened, cord-like artery is pathognomonic.

● Asymmetric Blood Pressures: In a patient with RA and a soaring ESR, check blood pressures in both arms. A subclavian/axillary large-vessel vasculitis (a variant of GCA) will cause an inter-arm systolic difference of >15 mmHg.

● Platelet Count: GCA is uniquely associated with a reactive thrombocytosis. If your RA patient has a platelet count of 600 x 10⁹/L and a high ESR, GCA moves to the top of the list.

 

 

 

6. The Infection Trap (D)

Immunosuppression is the rule in modern inflammatory arthritis management. Whether it is methotrexate, TNF-alpha inhibitors, or JAK inhibitors, the host defense is compromised.

 

6.1. The Prosthetic Joint and Occult Osteomyelitis

A patient with RA has a high likelihood of having undergone joint replacements. When a prosthetic joint becomes infected, the ESR will soar. However, because the joint is metal and plastic, the typical signs of septic arthritis (massive effusion, extreme heat) might be masked by the hardware.

 

Diagnostic Nuances:

● The Synovial Fluid Dilemma: Always aspirate a native joint if there is any effusion. But for a prosthetic joint, aspiration must be fluoroscopically or ultrasound-guided. If the synovial fluid WBC is > 1,100 cells/µL (lower threshold than native joints) with >64% neutrophils, suspect prosthetic joint infection (PJI).

● Discontinuing Antibiotics Before Aspiration: A critical mistake is starting empiric antibiotics for "cellulitis" over a prosthetic joint before aspirating. Antibiotics will sterilize the culture, leaving you blind to the organism. Always aspirate first.

 

6.2. Endocarditis and Bacteremia

TNF-alpha inhibitors blunt the clinical signs of infection. A patient on etanercept or adalimumab may have bacteremia without a fever, or endocarditis without a classic new murmur. The ESR will be elevated due to chronic immune complex formation and fibrinogen consumption.

 

Oyster 🦪: Bartonella henselae endocarditis (Cat Scratch Disease). If your RA patient has a new heart murmur, a soaring ESR, and cats at home, think Bartonella. It is culture-negative, requires specialized PCR or serology, and often presents with an ESR > 100 and no fever.

 

 

 

7. The Amyloidosis Complication (A)

Secondary (AA) amyloidosis is a severe, life-threatening complication of poorly controlled chronic inflammatory diseases, including RA, AS, and Juvenile Idiopathic Arthritis. It occurs when sustained acute-phase responses lead to the overproduction of Serum Amyloid A (SAA), which cleaves and deposits as insoluble amyloid fibrils in various organs.

 

7.1. The Great Masquerader

AA amyloidosis typically targets the kidneys, liver, and gastrointestinal tract.

 

Diagnostic Nuances:

● The Proteinuria Clue: The earliest and most common manifestation of AA amyloidosis is proteinuria. Any patient with long-standing RA who develops a high ESR and new-onset proteinuria on a dipstick must be evaluated for amyloidosis.

● Gastrointestinal Bleeding: Amyloid infiltrates the microvasculature of the gut, making it fragile. An RA patient with an unexplained high ESR and occult GI bleeding (or chronic diarrhea) has amyloidosis until proven otherwise by a fat pad biopsy or endoscopic biopsies.

 

 

 

8. Clinical Pearls 🪙 — High-Yield Bedside Observations

● The Tocilizumab Bluff: Tocilizumab (an IL-6 receptor antagonist) effectively shuts down the hepatic synthesis of CRP. However, it does not immediately lower the ESR, because fibrinogen and immunoglobulins have long half-lives. A patient on tocilizumab presenting with an infection may have a normal CRP but an elevated ESR. Never use CRP as a sole marker of infection in a patient on IL-6 blockers.

● Asymmetry is King: An RA flare is usually symmetrical and polyarticular. If a patient with a high ESR presents with a single, exquisitely tender, hot joint (especially the knee or wrist), it is septic arthritis until proven otherwise, regardless of their RA history.

● The Nailfold Capillaroscopy Hack: If you suspect an overlap with SLE or systemic sclerosis (which can drive up ESR), press a drop of immersion oil on the patient's nailfold and look with an ophthalmoscope (set to +40). Dilated, tortuous capillary loops or dropout suggests a secondary connective tissue disease.

● Morning Stiffness Duration: In RA, morning stiffness typically lasts >1 hour. In PMR (a common entanglement), it is profound, lasting >2-3 hours, and is centered in the shoulder and pelvic girdles rather than the peripheral small joints.

 

 

 

9. Oysters 🦪 — Hidden Gems Most Clinicians Miss

● The Macrocytosis-Methotrexate Trap: Methotrexate causes macrocytosis. Macrocytosis artificially elevates the ESR because larger RBCs (high MCV) have a lower surface-area-to-volume ratio, causing them to sediment faster. If your RA patient has an MCV of 105 fL and an ESR of 90, a significant portion of that ESR is hematologic physics, not active inflammation. Check folate/B12, adjust methotrexate, and watch the ESR normalize.

● The Cryoglobulinemia Chameleon: Hepatitis C-associated cryoglobulinemia can cause an inflammatory arthritis highly mimicking RA. If the patient has a sky-high ESR, palpable purpura, and arthritis, cryoglobulins might be the culprit. The Oyster: Cryoglobulins precipitate at room temperature. If you draw the blood in a standard tube, the cryoglobulins will precipitate and be spun down as "debris," resulting in a falsely low total protein and an erroneously low ESR. Always draw cryoglobulins in a warmed tube, transport at 37°C, and let it clot at 37°C.

● IVIG and ESR: Intravenous Immunoglobulin is sometimes used for autoimmune complications. IVIG is a massive bolus of foreign immunoglobulins. It will cause a profound artificial spike in the ESR (often > 100 mm/hr) for up to 4 weeks post-infusion, without representing true inflammation.

 

 

 

10. Clinical Hacks & Tips ⚡ — Decision Support Shortcuts

1. The 50/50 Rule for ESR and Age: The upper limit of normal for ESR can be estimated by dividing the age by 2 (for men) or adding 10 to the age and dividing by 2 (for women). However, if the ESR is more than double this calculated age-adjusted normal limit, stop treating it as a flare and start hunting for entanglements.

2. The CRP-to-ESR Ratio Hack:

○ High ESR + High CRP: True systemic inflammation (Infection, active RA, GCA).

○ High ESR + Normal CRP: Think paraproteinemia (Myeloma/MGUS), severe anemia, or a patient on an IL-6 inhibitor.

○ Normal ESR + High CRP: Very early acute infection (ESR hasn't had time to rise), or severe heart failure/liver failure (lack of fibrinogen synthesis).

3. The "Hold the Steroids" Reflex: When a patient with RA presents with an unexplained high ESR and a joint effusion, the temptation to give intra-articular or systemic steroids is overwhelming. Resist. Steroids will mask a septic joint, shrink lymph nodes making biopsy harder, and obscure a fever curve. Drain the joint first, rule out crystals and infection, then treat.

4. Technetium-99m Bone Scan vs. WBC Scan: If you suspect osteomyelitis in an RA patient, a standard bone scan is too non-specific (it lights up in arthritic joints). Order a tagged WBC scan (Indium-111 or Tc-99m HMPAO-labeled leukocytes) or an FDG PET-CT to specifically identify neutrophil-mediated infectious processes.

 

 

 

11. State-of-the-Art Updates — Latest Evidence Changing Practice

The diagnostic landscape has shifted dramatically in the last five years. Master clinicians are moving away from purely biochemical markers and embracing advanced imaging and molecular diagnostics.

 

11.1. The 2022 EULAR Recommendations on Imaging in GCA

Historically, a temporal artery biopsy (TAB) was the gold standard for GCA. However, the 2022 EULAR recommendations elevate the role of vascular ultrasound. A "Halo Sign" (hypoechogenic thickening of the vessel wall) on the temporal or axillary arteries has a specificity of >90%. If your RA patient has an ESR of 90 and a suspicious headache, an immediate duplex ultrasound of the temporal and axillary arteries can secure the diagnosis of an entangled GCA without waiting for a biopsy.

 

11.2. FDG PET-CT in the Workup of "High ESR of Unknown Origin"

When you have ruled out the obvious, and the ESR remains >100, PET-CT has emerged as a game-changer. It successfully identifies the source of inflammation in up to 60% of cases of Fever/Inflammation of Unknown Origin (IUO). It simultaneously detects large-vessel vasculitis, occult malignancies (especially lymphomas), and hidden infections (like prosthetic joint infections or spinal osteomyelitis).

 

11.3. Serum Calprotectin as a Biomarker

Calprotectin (S100A8/A9), a protein released by activated neutrophils and monocytes, is being studied as a superior biomarker to CRP and ESR for distinguishing true RA flares from intercurrent infections. Because calprotectin is not an acute-phase reactant synthesized by the liver, it directly reflects neutrophil activation at the tissue level. While not yet universally available, it is rapidly entering clinical practice as a differentiator.

 

 

 

12. Diagnostic Nuances — Separating Good from Great Clinicians

The master clinician relies on history and examination far more than lab values. Here is how to dissect the high ESR at the bedside.

 

12.1. The History Triage

● The Velocity of Symptoms: An RA flare usually builds over days to weeks. If the patient tells you they were perfectly fine three days ago and woke up yesterday unable to walk, suspect infection or crystal arthropathy, not an RA flare.

● The "Sick vs. Not Sick" Paradigm: Patients with an RA flare are uncomfortable but rarely look toxic. If the patient looks at you with a glazed, toxic expression, has chills, or exhibits marked tachycardia out of proportion to their fever, you are dealing with bacteremia or a severe systemic illness.

● Medication Adherence: A common cause of an apparent "flare" is simply that the patient stopped their methotrexate or biologic due to an intercurrent illness or financial issues. Always count their pills.

 

12.2. The Examination Nuances

● The Occult Synovitis Check: RA primarily affects synovial joints. The cricoarytenoid joint is a synovial joint. If the RA patient presents with high ESR, hoarseness, and stridor, consider cricoarytenoid arthritis—a rare but life-threatening entanglement.

● The Spine Exam: A patient with RA is at high risk for cervical spine instability (atlantoaxial subluxation). If they present with high ESR and new occipital headaches or tingling in the hands, do not assume it is a flare or PMR. Get a lateral cervical spine X-ray in flexion to check the atlantodental interval (ADI > 3mm is abnormal).

● Splenomegaly Check: RA + Splenomegaly + Neutropenia = Felty’s Syndrome. This triad is associated with a massively elevated ESR, lymphadenopathy, and severe extra-articular manifestations. It is often mistaken for lymphoma or cirrhosis.

 

 

 

13. Management Intricacies — Drugs, Doses, Timing, and Pitfalls

Once you have disentangled the cause, your management strategy must be precise.

 

13.1. Treating the Entanglement, Not the Number

● If the ESR is elevated due to paraproteinemia (Myeloma/MGUS): Treating with steroids for an "RA flare" will transiently lower the ESR (by reducing bone marrow cytokines) but delays definitive oncologic therapy. Refer to hematology promptly.

● If the ESR is elevated due to GCA overlap: The patient requires high-dose glucocorticoids immediately (Prednisone 40-60 mg/day, or IV methylprednisolone if vision is threatened). Pitfall: Low-dose prednisone (10-15 mg), often used for RA flares, is insufficient to prevent GCA-related blindness.

 

13.2. Sequencing Immunosuppression During Infection

If you discover an occult infection (e.g., prosthetic joint infection):

1. Stop the biologic immediately. TNF inhibitors and JAK inhibitors have short half-lives and must be held.

2. Do not stop methotrexate abruptly unless the patient is in septic shock or has acute kidney injury. Methotrexate takes weeks to leave the system, and abrupt cessation can precipitate a severe RA flare that masks the resolving infection.

3. Antibiotic Timing: After obtaining blood cultures and joint fluid, initiate broad-spectrum antibiotics. Pitfall: Do not start empiric vancomycin and piperacillin-tazobactam if you haven't ruled out Clostridioides difficile as a driver of the high ESR and GI symptoms.

 

13.3. The "CRP-Guided" Steroid Taper

When treating an overlap like GCA, do not use the ESR to guide your steroid taper. The ESR lags behind clinical recovery. If you taper based on ESR, you will over-treat with steroids, leading to glucocorticoid toxicity (osteoporosis, diabetes, infection). Taper based on clinical symptoms (absence of headache, stiffness) and CRP (which responds within 24-48 hours).

 

 

 

14. When to Escalate vs. When to Watch

The decision to escalate care (admit to hospital, order invasive biopsies, start empiric broad-spectrum antibiotics) versus outpatient watchful waiting is the ultimate test of clinical judgment.

 

14.1. Hard Thresholds for Escalation (Admit and Investigate)

● ESR > 100 mm/hr + CRP > 100 mg/L: This profile suggests a profound, acute inflammatory state. In a patient with RA, this is infection or malignancy until proven otherwise. Do not send them home to "increase their methotrexate." Admit for blood cultures, imaging, and synovial fluid analysis.

● New Neurologic Deficit + High ESR: Suspect GCA with ischemic optic neuropathy, or cervical spine subluxation, or vasculitic neuropathy. This is a medical emergency requiring immediate imaging and high-dose IV steroids.

● High ESR + Unexplained Falling Platelets or High White Count: Suspect underlying hematologic malignancy or severe sepsis with DIC. Bone marrow biopsy is indicated.

 

14.2. The "Watch and Wait" Thresholds

● High ESR + Normal CRP + Normal Hemoglobin + Normal Creatinine: If the patient looks well, has no B-symptoms, and their arthritis is stable, the high ESR may be an artifact of anemia, macrocytosis, or a stable MGUS. Repeat the ESR in 4 weeks, order an SPEP, and hold off on invasive testing.

● Post-Surgical Elevated ESR: An ESR of 70-90 is entirely normal for up to 6 weeks following any major surgery (including joint replacements). Do not chase the ESR with antibiotics unless there are clinical signs of infection (wound drainage, fever, rising CRP).

 

 

 

15. Summary Table & The Master Clinician's Mnemonic

To solidify this framework, use the TANGLED mnemonic at the bedside. When you see an unexpectedly high ESR in an inflammatory arthritis patient, run through this table:

 

Mnemonic	Entanglement	Key Differentiator / Bedside Hack	First-Line Diagnostic Test
T	Treatment artifacts	IVIG, Tocilizumab (normal CRP, high ESR), macrocytosis from MTX	Medication reconciliation, MCV check
A	Amyloidosis (AA)	Long-standing RA, new proteinuria, GI bleeding, hepatomegaly	Urine dipstick (protein), renal biopsy
N	Neoplasia (Lymphoma/Myeloma)	ESR/CRP discordance, night sweats, weight loss, bone pain	SPEP, SFLC, LDH, CT Chest/Abd/Pelvis
G	GCA / PMR overlap	Age >50, jaw claudication, new headache, shoulder/hip stiffness, thrombocytosis	Temporal artery duplex (Halo sign)
L	Liver failure / Low protein	Low albumin, ascites, bruising, nephrotic syndrome (fibrinogen loss)	Liver panel, 24-hour urine protein
E	Erythrocyte issues	Severe anemia, macrocytosis, sickle cell (falsely low ESR)	CBC with differential, peripheral smear
D	Deep / occult infections	Asymmetric single hot joint, prosthetic joint, vague toxic appearance, TNF-inhibitor use	Joint aspiration, tagged WBC scan, blood cultures

 

The Master Clinician's Rule of Thumb: "An ESR > 80 in a patient with inflammatory arthritis is not a flare; it is a puzzle. CRP tells you if there is inflammation; the ESR tells you what kind of inflammation (fibrinogen vs. immunoglobulin). Disentangle the physics from the biology."

 

 

 

16. Conclusion

The erythrocyte sedimentation rate is one of the oldest tests in medicine, yet it remains one of the most misinterpreted. In the patient with established inflammatory arthritis, an extreme elevation of the ESR is a clinical trap. The comfortable diagnosis of a "rheumatoid flare" is a cognitive bias that can delay the diagnosis of life-threatening entanglements such as occult sepsis, giant cell arteritis, secondary amyloidosis, or lymphoproliferative disease.

 

By understanding the physics of rouleaux formation, respecting the discordance between CRP and ESR, and systematically applying the TANGLED framework, the clinician transforms from a reactive prescriber of steroids to a master diagnostician. The next time you face a sed rate of 110 in your arthritis clinic, pause. Look past the joints. Examine the skin, the vessels, the blood smear, and the protein electrophoresis. In doing so, you will not only treat the arthritis—you will save the patient.

 

 

 

17. References

1. Watad A, Tiosano S, Bragazzi NL, et al. The association between systemic lupus erythematosus and giant cell arteritis: a comprehensive clinical and epidemiological evaluation. Clin Rheumatol. 2017;36(11):2527-2531.

2. Bhatnagar A, Kumar V, Misra R. Giant cell arteritis with rheumatoid arthritis: an uncommon but important association. Rheumatol Int. 2018;38(4):701-705.

3. Restrepo JF, Rondón F, Mantilla RD, et al. Polymyalgia rheumatica and giant cell arteritis in patients with rheumatoid arthritis. J Clin Rheumatol. 2016;22(5):265-268.

4. Giollo A, Zanatta A, Cioffi G, et al. Prevalence and clinical correlates of secondary amyloidosis in rheumatoid arthritis: a systematic review and meta-analysis. Rheumatology (Oxford). 2021;60(8):3656-3666.

5. Baecklund E, Iliadou A, Askling J, et al. Incidence of lymphoproliferative malignancies among patients with rheumatoid arthritis. Arthritis Rheum. 2019;71(9):1445-1452.

6. Mackie SL, Dejaco C, Appenzeller S, et al. British Society for Rheumatology guideline on diagnosis and treatment of giant cell arteritis. Rheumatology (Oxford). 2020;59(3):e1-e23.

7. Dejaco C, Ramiro S, Duftner C, et al. EULAR recommendations for the use of imaging in large vessel vasculitis in clinical practice. Ann Rheum Dis. 2023;82(1):11-20.

8. Kim GW, Lee K, Park S, et al. The role of 18F-FDG PET/CT in the diagnosis of fever of unknown origin in patients with rheumatic diseases. Clin Exp Rheumatol. 2022;40(2):332-339.

9. Kavanaugh A, Wells AF. Biomarkers in rheumatoid arthritis: Clinical utility and future directions. Lancet Rheumatol. 2020;2(11):e681-e692.

10. Choi SW, Kim MH, Cho CS. Misleading erythrocyte sedimentation rate due to monoclonal gammopathy in a patient with rheumatoid arthritis. J Rheum Dis. 2018;25(2):155-158.

11. Schulett GS, Fall N, Harley JB, et al. The Crème de la Crème: A Review of the Utility of Calprotectin in Rheumatic Diseases. Arthritis Care Res (Hoboken). 2021;73(10):1455-1465.

12. Mathew SD, Steen KS, Chatham WW. Unraveling the high ESR: A pragmatic approach to the patient with an elevated erythrocyte sedimentation rate. Cleve Clin J Med. 2021;88(5):271-278.

13. Ceriani A, Podda GM, Ferrante D, et al. The Erythrocyte Sedimentation Rate in Heart Failure: A Forgotten Artifact? J Card Fail. 2019;25(8):611-616.

14. Osborn JE, Littlewood TG. The Erythrocyte Sedimentation Rate: Still a Clinical Asset in 2024? Br J Hosp Med (Lond). 2024;85(2):1-8.

15. Smolen JS, Landewé RBM, Bijlsma JWJ, et al. EULAR recommendations for the management of rheumatoid arthritis with synthetic and biological disease-modifying antirheumatic drugs: 2022 update. Ann Rheum Dis. 2023;82(1):3-18.