Step 1: Visualise the skull film as a salt-and-pepper sprinkle - many fine lucent specks distributed across the calvarium, blurring the normal sharp tables.
Step 2: The driving mechanism is unchecked osteoclastic resorption. In primary hyperparathyroidism, raised PTH dissolves bone widely, and in the skull this leaves countless small radiolucent foci and patchy osteopenia, the textbook pepper-pot pattern.
Step 3: Distinguish the mimics. Multiple myeloma classically gives discrete punched-out or raindrop lytic deposits rather than a uniform granular sprinkle. Hyperthyroidism and pseudohyperparathyroidism do not feature this finding. So the speckled pepper-pot skull maps to hyperparathyroidism.
\[\boxed{\text{Hyperparathyroidism}}\]