Are Lines of Zahn pathognomonic for antemortem thrombosis? Yes—when defined as laminated platelet-fibrin bands formed in flowing blood. Other fibrin patterns may occur after death, but they are not true Lines of Zahn; no postmortem process reproduces the genuine pattern.

#pathognomonic #meded

Ovoid/popcorn-like soft-tissue calcifications suggest systemic sclerosis, but also occur in dermatomyositis, polymyositis/overlap disease, tumor calcinosis, tenosynovitis with psammomatous calcifications, and some cartilaginous tumors.

#pathognomonic #meded

Wickham striae mechanism. T-cell–mediated interface dermatitis. CD8+ T cells destroy basal keratinocytes, causing degeneration of the stratum basale and a lymphocytic infiltrate at the dermal-epidermal junction. Hypergranulosis and orthokeratosis follow, producing the striae.

#pathognomonic #meded

History of the pathognomonic finding in Aicardi syndrome: chorioretinal lacunae. They were thought to be scars left over from chorioretinitis, but Hoyt and colleagues’ 1978 paper showed it was a noninflammatory process in the retinal pigment epithelium and choroid.

#pathognomonic #meded

Sign spotlight: Gottron’s papules. Small, raised, flat-topped, pink-red to violaceous, scaly bumps that classically sit over the knuckles and other extensor joints of the hands. Think Dermatomyositis.

#pathognomonic #meded

Are Koplik spots pathognomonic for measles? Probably not. In a 2019 series of 717 patients labeled as having Koplik spots, PCR found measles in 202, rubella in 125, several other viruses, and no tested virus in 339. The major limitation: no photographs for validation.

#pathognomonic #meded

Here's strawberry gingivitis. In granulomatosis with polyangiitis, the threshold for ANCA-mediated autoimmune activity lowers, and that means tons of antigenic stimulation in places like the nose and mouth, leading to granulomatous inflammation.

#pathognomonic #meded