Errors in First Aid for the USMLE (2007): Musculoskeletal System

February 19, 2007

As always, this comes from an email sent to the First Aid team. Please add any errors or suggestions in the comments section.

Musculoskeletal (all references from Merck Manual and Robbins Basic Pathology)

  1. P.326, Smooth muscle contraction
    1. This diagram shows Myosin light-chain phosphatase (MLCP) acting before contraction. Every other reference I have found details SMC contraction in the following steps
      1. Calcium binds calmodulin
      2. Calcium-calmodulin activates Myosin light chain kinase (MLCK)
      3. MLCK phosphorylates myosin, allowing a crossbridge to form
      4. Contraction follows
      5. MLCP dephosphorylates myosin, allowing for relaxation.
    2. I think this diagram should be changed in the following way:
      1. “Cross-bridge formation with contraction
      2. After the action of MLCP, “contraction” should be changed to ” relaxation.”
  2. P.327, Rheumatoid arthritis
    1. In RA, the DIP is completely spared. A small point, but the image of the Swan-neck deformity should be pointing to the involved joint (hyper-extended PIP) and not the DIP (normal).
  3. P.327, Osteopetrosis
    1. In addition to be called “marble bone disease,” this condition is frequently referred to as “Albers-Schonberg” disease. I think this should be mentioned.
    2. Osteopetrosis also presents with hepatosplenomegaly (secondary hematopoiesis due to loss of bone marrow) and cranial nerve palsies. I think both of these should be mentioned.
  4. P.327, Osteitis fibrosa cystica
    1. This disease is also often referred to as “von Recklinghausen’s disease of bone.”
    2. In the same way that alkaline phosphatase is raised in states of high osteoblastic activity, Tartrate-Resistant Acid Phosphatase (TRAP) levels are raised in states of high osteoclastic activity. I think it is worth mentioning both of these correlates in this section.
  5. P.328, Polyostotic fibrous dysplasia
    1. This disease is often referred to as McCune-Albright. I think the text should be changed to “(McCune-) Albright Syndrome”
  6. P.329, Gout
    1. I think it would be helpful to include “glucose-6-phosphatase deficiency (von Gierke’s)“.
  7. P.330, Scleroderma
    1. After the first bullet point, I think it should say, “Associated with anti-Scl-70 antibody against topoisomerase“.
  8. P.331, Skin disorders
    1. Atopic dermatitis has pruritic eruptions within skin flexures, not on flexor surfaces i.e. you would expect to see them within the elbow crease and around the neck instead of on the surface of the bicep and forearm.
    2. Seborrheic keratosis should include the common vignette descriptions of “ stuck-on appearance” and “greasy.”
  9. P.332, Primary bone disorders
    1. A constant feature of osteoid osteoma (in contrast to osteoblastoma and osteoma) is complaint of pain at the site of the lesion. I think that this should be briefly mentioned: “pt. complains of pain”
    2. A feature of Giant Cell tumor of bone is the complaint of arthritis in a young person (20-40 yoa). I think this should be briefly mentioned: “young pt. complains of ‘arthritis'”.
    3. Osteosarcoma has a bimodal peak in incidence, once in 10-20 year olds associated with Retinoblastoma, and once in the elderly following Paget’s disease of bone. Without this distinction, it makes no sense so list Paget’s disease here because this rarely (if ever) occurs in patients younger than 40. I think this should be changed to:
      1. “Most common primary malignant tumor of bone. Peak incidence in men 10-20 years old (associated with familial retinoblastoma). Smaller second peak in elderly (associated with Paget’s disease of bone, bone infarcts, radiation). Commonly found….”
    4. A feature of Ewing Sarcoma is the complaint of pain and warmth over the site of the lesion. I think this should be briefly mentioned.
  10. P.333, Other ANCA-associated vasculitides
    1. In the same way that the “Lesions are of different ages” in PAN, I think it is worth mentioning that the lesions are all of the same age in microscopic polyangiitis.
  11. P.335, NSAIDS
    1. I do not understand why there is no mention of Aspirin in this section.
  12. P.337, Immunosuppresive agents: sites of action
    1. I do not understand why Tacrolimus (FK506) and Cyclosporine (CSA) are shown as having completely non-overlapping sites of action since they inhibit the exact same pathway at the exact same step (one by binding cyclophilin, the other by binding FKBP).

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