Cellulitis is common—and commonly misdiagnosed

Is it cellulitis or is it not? The bacterial skin and soft tissue infection is frequently seen in primary care, walk-in clinics and emergency departments, most often affecting a lower limb. But a red, swollen leg is not always cellulitis, and misdiagnosis is common.This is a key message from the CAEP 2024 Canadian ED Best Practices Checklist for Skin and Soft Tissue Infections, which notes that for cellulitis, physicians should rely on careful clinical assessment, avoid unnecessary bloodwork, imaging and hospital referral, and reserve IV antibiotics for patients who truly need them.Statistics for rates of cellulitis are not easy to come by, due to common misdiagnoses, but one Canadian study found more than 65,000 people were admitted for treatment over a four-year period.“Misdiagnosis is a big problem,” said lead author of the Checklist, Dr. Krishan Yadav, a clinician scientist with the Acute Care Research Program at the Ottawa Hospital Research Institute and associate professor with the department of emergency medicine at the University of Ottawa. These guidelines were created with patient partners with lived experience, infectious disease specialists, emergency physicians, an emergency nurse, an infectious diseases pharmacist, and knowledge translation scientists.“In the literature, up to one-third of patients may be misdiagnosed. Its mimics are venous stasis dermatitis, bursitis, gout, deep vein thrombosis . . . the list is long,” he said. The guidelines are summarized here. Dr. Yadav is also co-author of further research on the topic: Misdiagnosis of Uncomplicated Cellulitis: a Systematic Review and Meta-Analysis.Cellulitis is most often caused by Streptococcus pyogenes or Staphylococcus aureus. In certain patients, including those who are immunocompromised or have chronic wounds, gram-negative organisms or anaerobes may also be involved. The infection usually begins when bacteria enter through a break in the skin, such as a cut, insect bite, ulcer, abrasion, surgical wound, or a new tattoo or piercing. Sometimes no clear entry point is found.Risk factors for cellulitis include:diabetesa weakened immune systemlymphedema (swelling that stretches and cracks the skin)venous insufficiencyperipheral arterial diseaseThe Canadian Paediatric Society notes that social determinants of health, such as crowded housing conditions, act as community-level risk factors by increasing household colonization and transmission of bacteria like methicillin-resistant Staphylococcus aureus.Cellulitis usually presents with pain, erythema, warmth and swelling. It may also be associated with fever or lymphangitis. Although it can occur anywhere on the body, it most commonly affects a lower limb.“It is very uncommon to have bilateral symptoms—for example, both legs involved. In those circumstances, alternative diagnoses should be considered,” Dr. Yadav said.Indeed, the guidelines advise physicians to consider an alternative diagnosis in patients with bilateral symptoms, and not to use decision tools or specific investigations, such as white blood cell count or C-reactive protein, to make the diagnosis. “Cellulitis is primarily a clinical diagnosis,” with laboratory or imaging tests generally not needed.For non-purulent cellulitis, superficial wound swabs are not recommended, Dr. Yadav said. “And blood cultures should not be routinely ordered unless patients are systemically unwell. For example, if they have fever, lymphangitis, persistent tachycardia, tachypnea, hypotension—or if they are immunosuppressed. Routine blood tests, including inflammatory markers, should not be ordered for most cases of uncomplicated cellulitis.”The guidelines also note that imaging is also not routinely needed for uncomplicated cellulitis. But, a point-of-care ultrasound is recommended when there is uncertainty in differentiating cellulitis from a skin abscess. (See more on abscesses below). Imaging may also be considered in select other cases, including suspected osteomyelitis, foreign body or diagnostic uncertainty around necrotizing fasciitis. (But when necrotizing fasciitis is clinically suspected, imaging should not delay urgent surgical consultation.)Oral antibiotics are first-line treatment for most patients with uncomplicated cellulitis.“Most patients with cellulitis can be treated with oral (instead of intravenous) antibiotics,” Dr. Yadav said. “The vast majority can be treated outside of the hospital with oral antibiotics.” The guidelines also recommend physicians consider an oral NSAID for five to seven days as an adjunct to antibiotic treatment of patients with cellulitis. Hospital referralPatients should be referred to hospital for consideration of IV antibiotics if they are systemically unwell, cannot tolerate oral medicine because of vomiting or another issue, or have failed an adequate course of oral antibiotics, notes Dr. Yadav.“Patients should try to elevate the leg when possible if they have lower limb cellulitis. They should see a healthcare provider 72 hours after antibiotics have started if there is no improvement or some worsening. They should see a healthcare provider right away if they develop severe pain that seems out of proportion, or rapidly spreading painful erythema.”Necrotizing fasciitisThose warning signs need to be quickly addressed as they could be caused by necrotizing fasciitis. The guidelines advise clinicians to suspect it when there are signs of deeper tissue involvement, such as severe pain, a hard or “wooden” feel of the subcutaneous tissue, edema or tenderness beyond the erythema, systemic toxicity, altered mental status, crepitus, bullous lesions, skin necrosis or ecchymoses.In those cases, clinicians should not rely on imaging or blood tests to make the diagnosis. Immediate surgical consultation and IV antibiotics are required, and investigations should not delay treatment.AbscessesThe guidelines also distinguish cellulitis from uncomplicated purulent skin and soft tissue infections, such as skin abscesses. Abscesses may share features with cellulitis, such as pain, erythema, warmth, edema and induration, but they usually include a palpable area of fluctuance representing an underlying purulent collection. Point-of-care ultrasound can help when the diagnosis is uncertain and to identify the presence of underlying purulent collection in patients with skin abscesses.Treatment is incision and drainage (not needle aspiration). Routine packing of abscess cavities after incision and drainage is not recommended. Antibiotics are used as an adjunct in selected cases, including extensive surrounding cellulitis, systemic symptoms or immunosuppression.Bottom line, the latest guidelines indicate that after a sound diagnosis, most cellulitis can be managed without a hospital admission, IV antibiotics or extensive investigations, provided the patient is otherwise stable.

Cellulitis is common—and commonly misdiagnosed

Register for free access or login.

Related Topics