PANCE Blueprint Musculoskeletal (8%)

Osteomyelitis (ReelDx)



8-year-old with a non-healing wound on the leg

Patient will present as → a 54-year-old male with fever, chills, and pain in the left foot. His symptoms progressively worsened over the course of a week. Medical history is significant for poorly controlled type II diabetes mellitus. On physical exam, there is tenderness to palpation of the left foot. Laboratory testing is significant for an elevated erythrocyte sedimentation rate and C-reactive protein, as well as leukocytosis. Plain radiograph demonstrates periosteal thickening and soft tissue swelling.

An acute or chronic infection and inflammation of the bone and bone marrow; can occur because of hematogenous seeding, a contiguous spread of infection, or direct inoculation into intact bone (trauma or surgery)

  • Fever, restriction of movement of the involved extremity or refusal to bear weight, pain, or tenderness in the infected area, and signs of localized inflammation.
  • In patients with diabetes, classic signs and symptoms of infection may be masked due to vascular disease and neuropathy
  • Staphylococcus aureusmost common cause overall
  • Pasteurella multocidaseen in cases caused by cat and dog bites
  • Salmonella spp. in patients with sickle cell
  • Mycobacterium tuberculosis - can also be seen in cases of vertebral involvement (Pott disease)

Routine radiography is standard 1st-line imaging

  • Classic X-ray triad of demineralization, periosteal reaction, and bone destruction
    • Radiographic evidence of osteomyelitis lags behind symptoms and pathologic changes by 7 to 10 days
  • Magnetic resonance imaging (MRI) shows the changes before plain-film radiography or bone scan

Labs: CRP is usually elevated but nonspecific. WBC and ESR are high in most cases

  • A persistently elevated CRP (4–6 weeks) can be associated with persistent osteomyelitis
  • Definitive diagnosis is made by blood cultures or by needle aspiration/bone biopsy

Empiric therapy should be directed toward the most probable organism and tailored once cultural results are available. All hardware (if post-op) needs to be removed

  • Duration of therapy 4–6 weeks for acute osteomyelitis and generally >8 weeks for chronic osteomyelitis or MRSA infection
  • If a diabetic foot ulcer is larger than 2 x 2 cm or bone is palpable osteomyelitis is likely

osmosis Osmosis

Osteomyelitis is an infection of the bone that also affects the bone marrow and surrounding soft tissue. Staphylococcus aureus is the most common offending organism, although other organisms may cause osteomyelitis as well. Osteomyelitis persisting longer than one month is considered chronic. Patients with this condition experience constant bone pain that is unrelieved by rest and is worsened with activity. Other symptoms of osteomyelitis include local warmth and edema at the site of infection, fever, chills, nausea, night sweats, and restlessness. Treatment of osteomyelitis includes antibiotic therapy and surgical removal of poorly vascularized tissue and/or necrotic bone. Hyperbaric oxygen may also be used in patients with chronic osteomyelitis that is refractory to treatment.

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Staphylococcus aureus
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Congratulations - you have completed OSTEOMYELITIS osteomyelitis. You scored %%SCORE%% out of %%TOTAL%%. Your performance has been rated as %%RATING%%
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Question 1
A 66-year-old male presents to his primary care physician complaining of increasing discharge from an ulcer on the plantar aspect of his right great toe seen here. He has a long history of poorly controlled diabetes with complications including chronic renal failure and bilateral peripheral neuropathy to the mid-calf. He denies any pain or fevers/chills. Examination confirms warmth and erythema of the area surrounding the ulcer. A probe can be passed into the ulcer; however, it is not readily apparent if bone can be contacted with the probe. Laboratory evaluation is significant for a WBC count of 17k/uL and an ESR of 116 mm/h. Which of the following would be the most accurate diagnostic test for this patient's condition?
Three-phase bone scan of the foot
A nuclear medicine bone scan may detect osteomyelitis much earlier than plain radiographs; however, it is relatively nonspecific and makes differentiating osteomyelitis from other pathologic conditions difficult.
Ultrasound of the great toe
Ultrasound has numerous benefits in detecting osteomyelitis, such as real-time imaging and avoidance of radiation and contrast dye. However, MRI is the preferred diagnostic modality because of its improved image quality and soft-tissue detail.
AP and lateral radiographs of the foot
Radiographs may show periosteal elevation and other signs suggestive of osteomyelitis; however, these signs may lag behind the disease onset by weeks and are not as reliable as MRI findings. However, radiographs should be the first imaging study ordered prior to an MRI.
MRI of the foot
CT scan of the foot
Although CT scans may show osseous changes of osteomyelitis earlier than plain radiographs; MRI is still the preferred modality for diagnosis due to its improved soft-tissue visualization.
Question 1 Explanation: 
This patient is suffering from osteomyelitis secondary to a diabetic foot infection. MRI is the most accurate diagnostic imaging test for osteomyelitis.
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References: Merck Manual · UpToDate

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