A 61-year-old man presents to the emergency room with a painful, swollen left leg. He states that his symptoms began that morning after a long flight from Australia. He denies shortness of breath, chest pain, or cough. On review of systems, he notes that he has been constipated recently and had several episodes of bright red blood per rectum. He has not noticed any weight loss, fevers, or night sweats. He has a past medical history of a deep vein thrombosis 4 years ago during a hospitalization for community acquired pneumonia and was treated with warfarin for 3 months afterward. He also has chronic hepatitis C from previous intravenous drug use. The patient has a 30 pack-year smoking history and has never had a colonoscopy. His father is 84-years-old and has chronic kidney disease from diabetes, and his mother passed away from a massive pulmonary embolus when pregnant with his younger sister. In the emergency room, his temperature is 98.7°F (37.1°C), blood pressure is 142/85 mm/Hg, pulse is 79/min, and respirations are 14/min. On exam, he is in no acute distress. His left calf is larger in caliber than the right calf which is red and tender to palpation. Dorsiflexion of the foot worsens the pain. His abdomen is soft, nontender, and nondistended without hepatomegaly. The remainder of the physical exam is unremarkable. Labs are shown below: Hemoglobin: 13.0 g/dL Leukocyte count: 6,000/mm^3 Platelets: 160,000/mm^3 Aspartate aminotransferase: 15 U/L Alanine aminotransferase: 19 U/L Alkaline phosphatase: 81 IU/L Hepatitis C antibody: reactive Hepatitis C titer: 0 copies/mL Which of the following is the most likely cause of this patient’s condition?

Resistance of factor V to inactivation by protein C

Loss of antithrombin III in urine

A 69-year-old male presents to the emergency room with back pain. He has a history of personality disorder and metastatic prostate cancer and was not a candidate for surgical resection. He began chemotherapy but discontinued due to unremitting nausea. He denies any bowel or bladder incontinence. He has never had pain like this before and is demanding morphine. The nurse administers IV morphine and he feels more comfortable. Vital signs are stable. On physical examination you note tenderness to palpation along the lower spine, weakness in the bilateral lower extremities, left greater than right. Neurological examination is also notable for hyporeflexia in the knee and ankle jerks bilaterally. You conduct a rectal examination, which reveals saddle anesthesia. Regarding this patient, what is the most likely diagnosis and the appropriate next step in management?

The most likely diagnosis is cauda equina syndrome and steroids should be started prior to MRI

The most likely diagnosis is cauda equina syndrome and the patient should be rushed to radiation

The most likely diagnosis is conus medullaris syndrome and steroids should be started prior to MRI

The most likely diagnosis is conus medullaris syndrome and steroids should be started after MRI

The most likely diagnosis is cauda equina syndrome and steroids should be started after MRI

A 35-year-old male presents to his primary care physician with pain along the bottom of his foot. The patient is a long-time runner but states that the pain has been getting worse recently. He states that when running and at rest he has a burning and aching pain along the bottom of his foot that sometimes turns to numbness. Taking time off from training does not improve his symptoms. The patient has a past medical history of surgical repair of his Achilles tendon, ACL, and medial meniscus. He is currently not taking any medications. The patient lives with his wife and they both practice a vegan lifestyle. On physical exam the patient states that he is currently not experiencing any pain in his foot but rather is experiencing numbness/tingling along the plantar surface of his foot. Strength is 5/5 and reflexes are 2+ in the lower extremities. Which of the following is the most likely diagnosis?

Common fibular nerve compression

Red flags in musculoskeletal complaints for USMLE Step 2 CK: High-Yield Diagnosis Lessons

Red Flags in MSK - Spotting the Sirens

Red Flags for Spine Conditions

Systemic Signs:
- Unexplained weight loss (>10 lbs in 3 months)
- Fever, night sweats, chills
- History of malignancy (Prostate, Breast, Kidney, Thyroid, Lung - 📌 PB KTL)
Neurologic Deficits:
- Saddle anesthesia (numbness in groin/buttocks)
- Bowel or bladder incontinence/retention
- Progressive, bilateral motor weakness or gait ataxia
Other Major Warnings:
- Age >50 or <20 with new-onset pain
- Severe, constant, progressive non-mechanical pain (pain at rest)
- Recent significant trauma or IV drug use

⭐ Cauda Equina Syndrome: A critical diagnosis to not miss. The combination of saddle anesthesia, plus bowel/bladder dysfunction, is highly specific and requires emergent MRI and surgical evaluation.

Back Pain Red Flags - Spinal Cord Alarms

Suspect serious spinal pathology when a patient with back pain presents with certain "red flag" symptoms. These warrant immediate investigation to rule out conditions like cauda equina syndrome, spinal infection, fracture, or malignancy. Prompt recognition is critical.

📌 Mnemonic: TUNA FISH

Letter	Red Flag
T	Trauma, Thoracic pain
U	Unexplained weight loss
N	Neurological symptoms (e.g., saddle anesthesia)
A	Age > 50 years
F	Fever, chills
I	IV drug use, Immunosuppression
S	Steroid use (chronic)
H	History of cancer

⭐ Cauda Equina Syndrome (CES) is a dire surgical emergency. Key signs include bilateral sciatica, severe/progressive neurologic deficit in the legs, saddle anesthesia, and new-onset bowel/bladder dysfunction. Delayed treatment can lead to permanent paralysis.

Immediate Management Flowchart

Limb & Joint Red Flags - Peripheral Warnings

Septic Arthritis: Medical emergency!
- Acute onset, single swollen, painful joint.
- Systemic symptoms: fever, chills, malaise.
- Inability to bear weight.
- Synovial fluid: WBC > 50,000/mm³, >75% neutrophils.
Compartment Syndrome: Surgical emergency!
- Pain out of proportion to injury; severe pain on passive stretch.
- Tense, swollen, shiny skin over the compartment.
- 📌 6 P's (late signs): Pain, Pallor, Paresthesia, Pulselessness, Poikilothermia, Paralysis.
Deep Vein Thrombosis (DVT)
- Unilateral limb swelling, warmth, erythema, and tenderness.

⭐ In suspected compartment syndrome, a delta pressure (Diastolic BP − Compartment Pressure) of < 30 mmHg is a strong indication for fasciotomy.

High‑Yield Points - ⚡ Biggest Takeaways

Constitutional symptoms (fever, night sweats, weight loss) raise suspicion for malignancy or infection.

Focal neurologic deficits (weakness, numbness) suggest spinal cord or nerve root compression.

Bowel or bladder incontinence and saddle anesthesia are critical signs of cauda equina syndrome.

A personal history of cancer is a major red flag for metastatic disease.

Nocturnal pain or pain unrelieved by rest points towards tumor or infection.

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