Cellulitis Mimics

Introduction
Cellulitis is often misdiagnosed in ED. Available literature reports a misdiagnosis rate of close to 30% that leads to unnecessary admission and antibiotics. 

Cellulitis usually doesn’t affect the deeper layers of skin and presents is a poorly demarcated area of superficial bacterial infection which is painful, erythematous and warm to the touch. It is a clinical diagnosis and no labs are needed unless there are other concerns (Nec Fasc, Osteomyelitis, Abscess). Blood cultures are low yield and should be done only in critically ill and those who fail to improve. Most cases of cellulitis are due to direct inoculation and it is rare for both extremities to be affected at the same time. BILATERAL CELLULITIS IS RARE. Also, cellulitis should be painful rather than itchy. If it is chronic, it is not cellulitis.

Erythema that spreads past drawn margins does not always mean that the patient is worsening. Erythema of cellulitis can spread in the first 48 hours as a normal progression and this does NOT always indicate treatment failure. Think escalation of Antibiotics if erythema is more intense or patient is more ill-appearing or persistent fever.

Common Organisms: Streptococcus pyogenes and Staphylococcus aureas in immunocompetent, without cirrhosis, neutropenia or other risk factors. Purulence or drainage should make you think about staph and consider MRSA in purulent cellulitis if there are risk factors associated. Penicillins or first-generation cephalosporin is a good first choice. Options for MRDA include Sulfamethoxazole/trimethoprim, linezolid, and doxycycline.

(Broad-spectrum antibiotics should be used in critically ill, high risk fo uncommon organismsHigh risk for resistant bacteria)


Mimics

• DVT - Usually differentiable on history and exam
• Stasis Dermatitis - Usually bilateral but can be unilateral as well. Usually due to underlying bilateral venous insufficiency. Leaked out fluid irritates the skin and causes redness. It may be acute (appears and feels as bilateral cellulitis) or chronic (thick hyperpigmented skin with hemosiderin deposits).
• Lipodermatosclerosis. This looks like erysipelas and commonly seen in patients with chronic venous insufficiency. It tends to occur on the medial aspect of the ankle. This can be treated with low dose steroids.
• Necrotising Fasciitis - Pain out of proportion of exam and pain extending beyond the borders of erythema. Most patients are ill-looking with unstable vital signs. Other possible features are insensate skin overlying the area of infection, “Dishwater-appearing fluid” drainage from within the wound. Erythema will often progress rapidly, even within hours. Admit for observation if any concerns for NF. 
• Contact dermatitis presents with pruritis which is a response to an external exposure seen the site of the exposure.
• Dermatohypersensitivity reaction. Allergic-type reaction due to bites, viral infections, medications. 
• Lymphedema, gout and erythema migrans. Usually differentiated based on history
• Calciphylaxis - This is a painful, relapsing and remitting condition which is often seen in cases ofunderlyingg renal failure, diabetes, obesity, liver disease or are taking warfarin. Calcium deposition in blood vessels of the dermis causes skin necrosis and lead to eschars over adipose areas. 

Venous stasis and lymphedema predisposes to cellulitis. 

If on elevating the legs for 1-2 mins, erythema goes away then it is less likely to be cellulitis

Oral v/s IV Antibiotics for Cellulitis

There is good evidence that oral antibiotics are just as good across a wide range of con- ditions such as cellulitis, pneumonia, pyelonephritis, osteomyelitis and even endocarditis. Majority of patients with uncomplicated cellulitis do well with oral antibiotics. 

Take Home

• Think about alternative diagnoses for erythema and warmth
• Bilateral lower extremity cellulitis is rare
• If on elevating the legs for 1-2 mins, erythema goes away then it is less likely to be cellulitis
• When discharging on oral antibiotics, review high risk patients in 48-72 hours 

References:

• Raff AB, Kroshinsky D. Cellulitis: a review. JAMA. 2016; 316(3): 325-37.
• McCreary EK, Heim ME, Schulz LT, et al. Top 10 myths regarding diagnosis and treatment of cellulitis. J Emerg Med. 2017 Oct; 53(4): 485-492.
• Aboltins, CA et al. Oral versus parenteral antimicrobials for the treatment of cellulitis: a randomized non-inferiority trial. J Antimicrob Chemother. 2015 Feb;70(2):581-6.
  PMID: 25336165
  
  
  
  

  Posted by:

  
  

  

                

       Lakshay Chanana

       

       ST4 Trainee

       Royal Infirmary of Edinburgh

       Department of Emergency Medicine

       Edinburgh

       Scotland

  
  

       @EMDidactic