USMLE Step 1 Question 358

Question:

A 53-year-old man presents to the emergency room with fever, complaining of several weeks of lower thoracic spinal pain, erythema, and swelling. Chest x-ray reveals loss of intervertebral space with vertebral collapse, as well as a cavitary lesion in the right apical lung field. What is the most likely pathology of his complaint?

Correct Answer: D.  Mycobacterium tuberculosis via hematogenous spread

This patient is suffering from tuberculous osteomyelitis of the spine (Pott’s disease). Although these patients often present with a clear chest x-ray, pulmonary lesions suggestive of tuberculosis help confirm the diagnosis. Lumbar and lower thoracic vertebrae are common sites of hematogenous targets, owing to their dense vascularization, making Mycobacterium tuberculosis via hematogenous spread (choice D) the correct answer.

Decreased osteoblast activity with normal osteoclast activity (choice A) is seen in primary osteoporosis type 2 (“senile osteoporisis”), which occurs in patients over 60 of both genders.

Haemophilus influenType I collagen defect via hematogenous spread (choice B) is a potential cause of vertebral osteomyelitis, it is unlikely in a patient with concomitant tuberculosis.

Mycobacterium tuberculosis via direct extension (choice C) is unlikely, as it would require the lesion to spread through lung parenchyma, into the pleural space, and through the parietal pleura. The discontinuous nature of the pulmonary and vertebral lesions (apical vs. low thoracic) further discounts this possibility.

A type I collagen defect (choice E) would be seen with genetic disorders like osteogenesis imperfecta (OI). Ehlers-Danlos Syndrome (EDS) HAS TYPE 3 COLLAGEN DEFECT. In OI, fractures are usually found in the long bones, ribs, and small bones of the hands and feet. The classic symptom of EDS is joint laxity, manifested by dislocations and subluxations. Neither disorder would present with signs of infection.