Family History and a Preoperative Workup

Correct answer: B. Recurrent laryngeal nerve

• A. Incorrect. The hypoglossal nerve supplies the intrinsic and most extrinsic tongue muscles. Injury causes tongue deviation toward the affected side, not hoarseness.
• B. Correct. The recurrent laryngeal nerve supplies all intrinsic laryngeal muscles except the cricothyroid, and it runs in the tracheoesophageal groove immediately adjacent to the thyroid gland. Unilateral injury paralyzes a vocal cord and produces the breathy hoarseness described; bilateral injury threatens the airway.
• C. Incorrect. The glossopharyngeal nerve carries sensation and taste from the posterior third of the tongue and motor supply to the stylopharyngeus. Injury affects swallowing and the gag reflex.
• D. Incorrect. The external branch of the superior laryngeal nerve supplies the cricothyroid and is also at risk in thyroid surgery, but injury produces loss of vocal pitch range and voice fatigue rather than frank hoarseness.

Correct answer: B. Autoimmune destruction of oligodendrocytes causing demyelination in the central nervous system

• A. Incorrect. Schwann cells myelinate peripheral nerves. Autoimmune attack on peripheral myelin describes Guillain-Barré syndrome and chronic inflammatory demyelinating polyneuropathy.
• B. Correct. Multiple sclerosis is a T cell-mediated autoimmune attack on central nervous system myelin and the oligodendrocytes that produce it. Demyelinated plaques disseminated in space and time produce the characteristic relapsing-remitting pattern of neurologic deficits.
• C. Incorrect. Loss of dopaminergic neurons in the substantia nigra describes Parkinson disease, producing bradykinesia, resting tremor, and rigidity.
• D. Incorrect. Antibodies against the acetylcholine receptor describe myasthenia gravis, which causes fatigable weakness that worsens with sustained activity.

Note: Dental relevance: trigeminal neuralgia occurring in a young patient should raise suspicion of multiple sclerosis, since a demyelinating plaque at the trigeminal root entry zone is a recognized cause. Short morning appointments help, since fatigue and heat sensitivity worsen symptoms later in the day.

Correct answer: A. 50%

• A. Correct. Duchenne muscular dystrophy is X-linked recessive. A carrier mother has one affected and one normal X chromosome, and each daughter inherits one of them at random along with a normal X from her father. Each daughter therefore has a 50% probability of being a carrier.
• B. Incorrect. Twenty-five percent is the probability that any given child — counting both sexes — will be a carrier daughter, since it combines a 50% chance of being female with a 50% chance of inheriting the affected X. Read carefully for whether the question specifies a daughter or a child.
• C. Incorrect. All daughters would be carriers only if the father were affected, since he would pass his single affected X to every daughter.
• D. Incorrect. Seventy-five percent does not correspond to any outcome in this cross.

Note: Full cross for a carrier mother and unaffected father: 25% affected son, 25% unaffected son, 25% carrier daughter, 25% unaffected daughter.

Correct answer: C. Activated partial thromboplastin time

• A. Incorrect. Prothrombin time assesses the extrinsic pathway — factor VII — and is normal in hemophilia A. It is used to monitor warfarin and to assess hepatic synthetic function.
• B. Incorrect. Bleeding time reflects platelet function and vascular integrity. It is prolonged in von Willebrand disease and thrombocytopenia, but is normal in hemophilia A since platelets are unaffected.
• C. Correct. Hemophilia A is a deficiency of factor VIII, a component of the intrinsic pathway, which the activated partial thromboplastin time measures. It is prolonged, while prothrombin time, bleeding time, and platelet count all remain normal.
• D. Incorrect. Platelet count is normal. Hemophilia is a coagulation factor deficiency, not a platelet disorder.

Note: A clean way to remember it: PT and the extrinsic pathway go with warfarin; PTT and the intrinsic pathway go with heparin and with hemophilia. Both hemophilia A (factor VIII) and hemophilia B (factor IX) prolong the PTT.

Correct answer: C. Reversible, non-selective inhibition of cyclooxygenase

• A. Incorrect. 5-lipoxygenase inhibition describes zileuton, used in asthma to block leukotriene synthesis. It is not an analgesic.
• B. Incorrect. Selective COX-2 inhibition describes celecoxib, which spares gastric mucosal prostaglandin synthesis but carries increased cardiovascular risk.
• C. Correct. Ibuprofen competitively and reversibly inhibits both COX-1 and COX-2, reducing prostaglandin synthesis. This produces its analgesic, anti-inflammatory, and antipyretic effects, and the reversibility means platelet function recovers as the drug is cleared.
• D. Incorrect. Irreversible cyclooxygenase inhibition describes aspirin, which acetylates the enzyme permanently. Because platelets cannot synthesize new enzyme, the antiplatelet effect persists for the platelet lifespan of 7 to 10 days.

Note: Interaction worth noting: ibuprofen competes with aspirin for the platelet COX-1 binding site and can blunt aspirin’s cardioprotective effect if taken beforehand.