Rhabdomyolysis and hyperkalemia: the unnamed disease

The scenario never names the disease, and the first instruction is to explain *the disease highlighted in the scenario* — so identifying it is the first mark and everything else depends on getting it right. The findings converge: naloxone reversed the presentation, which means an opioid overdose; the roommate does not know how long the patient was lying there, which means a prolonged period of immobility; necrotic tissue sits over the greater trochanter and the forearm, which are pressure points against a hard surface; the electrocardiogram shows a prolonged PR interval with peaked T waves; and the potassium is 6.9. That is rhabdomyolysis from pressure-induced muscle necrosis, with severe hyperkalaemia as its most immediately lethal consequence. Name it in the first sentence and say which findings you named it from, because a post that describes the mechanism without ever stating the diagnosis reads as though it guessed.

The genetics bullet is the trap, and how you handle it separates a strong post from an adequate one. This patient's rhabdomyolysis is acquired — pressure, ischaemia and time did it, not an inherited defect — so the tempting answer is that genetics played no role. That answer is correct and incomplete. The version that earns the mark names what genetics *can* contribute and then excludes it: McArdle disease, where a phosphorylase deficiency starves exercising muscle of glucose; carnitine palmitoyltransferase II deficiency, where fatty acid oxidation fails under stress; malignant hyperthermia susceptibility, where a calcium release channel misbehaves. Each of these produces recurrent rhabdomyolysis, and none of them fits a patient found unresponsive after an overdose. Naming the differential and ruling it out on the evidence is what the bullet is actually testing. The exclusion also strengthens the final bullet, since an inherited myopathy is one of the characteristics that would genuinely change the response.

*Why the patient is presenting with the specific symptoms described* wants the electrocardiogram explained, not merely reported. Raised extracellular potassium reduces the gradient across the myocyte membrane and brings the resting membrane potential closer to threshold. Repolarisation accelerates first, which is why the T waves are tall and peaked and why that is the earliest change. As the potassium rises further the resting potential stays partially depolarised, fast sodium channels are progressively inactivated, and conduction slows — which is the prolonged PR interval and, at higher levels still, a widening QRS. At 6.9 the patient is in the range where these changes are expected and the trajectory matters more than the number. The burning pain over the hip and forearm belongs to the muscle injury itself rather than to the potassium. Saying which change comes first and which arrives later also shows that the tracing is being read as a trajectory rather than a snapshot.

The cells bullet has three answers, and most posts give one. Skeletal myocytes are where it starts: sustained pressure cuts perfusion, ATP falls, the sodium-potassium pump fails, sodium and then calcium flood into the cell, calcium-dependent proteases and phospholipases activate, and the sarcolemma gives way — releasing potassium, myoglobin, creatine kinase and phosphate into the extracellular fluid. Cardiac myocytes are the second, because they are where the released potassium does its damage to conduction. Renal tubular epithelium is the third, since filtered myoglobin precipitates in the tubules, causes direct toxicity and vasoconstriction, and turns a muscle injury into acute kidney injury. Naming all three shows you have followed the potassium and the myoglobin out of the muscle rather than stopping at the lysis. Following the potassium and the myoglobin out of the muscle is what turns a description of cell death into an account of a systemic illness.

The final bullet asks how another characteristic would change your response, and the two examples the brief offers — gender and genetics — are worth answering with something measurable rather than a gesture. Muscle mass is the honest variable behind the gender example: more skeletal muscle under pressure means a larger potassium and myoglobin load released for the same duration of compression, so a heavily muscled patient can present with a higher potassium and a greater risk of pigment nephropathy from an identical period down. Age changes renal reserve and therefore how quickly the kidney fails. A statin, an existing myopathy, or sickle cell trait each lowers the threshold at which muscle breaks down. Pick one, say what it changes, and say what you would do differently because of it. Stating what you would monitor or treat differently is what converts the observation into a clinical response, which is what the bullet asks for.