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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 12h

From the pages of Pathognomonic Signs of Disease: Giant cytoplasmic granules in leukocytes. These are oversized azurophilic inclusions on Wright-Giemsa smear, especially in neutrophils. This is a historically pathognomonic finding for Chédiak-Higashi syndrome. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 05/10/2026

Are Call–Exner bodies pathognomonic for granulosa cell tumor? Not strictly. “Call–Exner-like” spaces may contain mucin or other eosinophilic material instead of basal lamina material as in true Call-Exner bodies. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 02/10/2026

An Inflamed DIP joint means swelling plus redness at the distal interphalangeal joint (not just bony enlargement). It's an important clue to psoriatic arthritis, but also happens in gout, pseudogout, and erosive osteoarthritis. This and others at pathognomonic.com #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 01/10/2026

Choroid tubercle mechanism: Hematogenous tuberculosis seeds the choroidal vasculature, where granulomatous inflammation produces pale yellow choroidal lesions. The choroid is so susceptible in part because it has the highest blood flow per unit tissue in the body. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 30/09/2026

Dutch ophthalmologist Jan van der Hoeve coined the term "phakoma" in 1923 after the Greek phakos for ""lentil,"" as he observed multiple "mother spots" and round birthmarks on patients with tuberous sclerosis. Retinal phakoma are considered pathognomonic for the disease. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 29/09/2026

Lisch Nodules: Small, dome-shaped, well-defined tan to brown raised spots on the surface of the iris, typically multiple, smooth, and visible on slit-lamp eye exam rather than to the naked eye. The academy tells us this automatically points to neurofibromatosis type 1. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 28/09/2026

Is erythema migrans pathognomonic for Lyme disease? Well, no. STARI can produce an indistinguishable expanding rash, and similar lesions occur with Asian tick-associated rash illness; tick saliva may sometimes cause the eruption without Borrelia. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 25/09/2026

PAS-positive macrophages point to Whipple’s disease. Key mimic: MAC, which is PAS-positive but acid-fast positive; T. whipplei is acid-fast negative. Rhodococcus and fungi can also complicate specificity. That's why this is not truly pathognomonic. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 24/09/2026

Burton’s line mechanism: Lead in gingival capillaries reacts with hydrogen sulfide made by oral anaerobic bacteria, depositing dark lead sulfide at the gumline. It's an elegant intersection chemistry, toxicology, and microbiology. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 23/09/2026

The moment anterior lenticonus enters the pathognomonic arena: A paper published in 1966 by Arnott, Crawfurd, and Toghill details a case report and in-depth literature review linking anterior lenticonus as a specific sign of Alport’s syndrome. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 22/09/2026

Pneumatosis intestinalis: linear or bubbly gas within the bowel wall on abdominal imaging. When this pattern appears in preterm neonates, necrotizing enterocolitis should move high on the differential. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 21/09/2026

Is electrical alternans pathognomonic for a large pericardial effusion? Not even close. It also occurs with rapid supraventricular rhythms, myocardial ischemia, intermittent bundle or fascicular block, hypertrophic cardiomyopathy, severe hypocalcemia, and drug toxicity. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 18/09/2026

Howell–Jolly bodies are nuclear remnants inside RBCs, seen during hyposplenia. A worthwhile association to know, but far from pathognomonic. They also show up in certain chemotherapies and corticosteroids, megaloblastic anemia, myelodysplastic syndrome, and hemolytic anemia. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 17/09/2026

Bilateral conjunctival suffusion, the hallmark of leptospirosis...on exams. Its mechanism: Leptospira injures conjunctival endothelium and loosens junctions, causing vascular leak and red eyes without purulent conjunctivitis. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 16/09/2026

Entamoeba histolytica has infected humans since prehistoric times. The earliest confirmed detections of E. histolytica come from Neolithic sites in Switzerland dating to approximately 3700 to 3400 B.C.E., with additional evidence from ancient Greece and Bronze Age France. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 15/09/2026

Maltese crosses in RBCs: four small pear-shaped intraerythrocytic forms radiate from a central point on Giemsa/Wright stain. Pathognomonic for babesiosis? Almost, but there's an edge case that violates strict pathognomony. Its name is Theileria. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 14/09/2026

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

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 11/09/2026

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

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 10/09/2026

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

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 09/09/2026

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

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 08/09/2026

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

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 07/09/2026

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

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 04/09/2026

Eosinophiluria: eosinophils in urine, classically taught with drug-induced acute interstitial nephritis, but the specificity really isn't there.. It is a memorable association, but not strong enough to be treated as pathognomonic in isolation. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 03/09/2026

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

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 02/09/2026

The first histological description of pulmonary hamartoma goes to German physician and naturalist Herbert Lebert in 1845, who wrote about a pulmonary cartilage tumor. The link between this benign tumor and pulmonary popcorn calcification on radiology came in 1948. #pathognomonic #meded"

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 01/09/2026

Here's raindrop skull: On cranial x-ray, multiple, well-defined, round "punched-out" lytic lesions scattered throughout the skull vault, without sclerotic margins or periosteal reaction, producing a raindrop-like appearance. NOT the same as pepperpot! Think Multiple myeloma. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 31/08/2026

Is the molar tooth sign pathognomonic for Joubert syndrome like the books say? No. It also appears in Dekaban–Arima, Senior–Løken, COACH, orofaciodigital type VI, polymicrogyria, and related syndromes. That is why the broader category is now Joubert syndrome–related disorders. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 28/08/2026

Non-caseating small-bowel granulomas most commonly suggest Crohn’s disease, but don't go thinking they are pathognomonic! Other causes include sarcoidosis, CVID enteropathy, mycobacteria, Yersinia, Whipple’s, fungi, parasites, drugs, lymphoma, and malignancy reactions. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 27/08/2026

The Simmonds-Thompson test mechanism: Squeezing the calf causes the muscles to shorten, pulling on the Achilles and making the foot plantarflex. An interruption in the transmission of that force, such as when the tendon is torn, results in no movement. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 26/08/2026

History tidbit. The term that stuck for this finding's disease, sclerosing cholangitis, was introduced by American pathologist Benjamin Castleman in 1954. He would also publish the first case series on protein alveolar proteinosis, and have Castleman disease named after him #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 25/08/2026

Observe the Aschoff body. Most commonly seen in the myocardium, Aschoff bodies are foci of fibrinoid necrosis surrounded by T-lymphocytes, plasma cells, Anitschow cells, and Aschoff cells. Pathognomonic for rheumatic heart disease and rheumatic fever. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 24/08/2026

Are Negri bodies pathognomonic for rabies? Close, but not strictly. Rabies-like neuronal inclusions have been found in a non-rabid man and in a child with Reye syndrome; immunofluorescence and electron microscopy were negative. Light microscopy alone cannot establish rabies. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 21/08/2026

Short vid: Mechanism Minute-> Larva currens instagram.com/mariocaldararomd tiktok.com/@mariocaldararomd youtube.com/@MarioCaldararoMD facebook.com/pathognomonicsignsofdisease

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 21/08/2026

The continuous machinery murmur. A murmur persisting through systole and diastole. Classically from PDA. Also: ruptured sinus of Valsalva, coarctation w collaterals, coronary artery fistula, pulmonary AVM, and mammary arterial souffle of pregnancy or lactation. #pathognomonic #meded"

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 20/08/2026

Silver stool mechanism. The ampullary mass bleeds leading to melena, while also obstructing the outflow of bile from the CBD. The dark color of melenic stool combines with the pallor of acholia to create a silver color. Essentially, melenic stool + pale stool = silver stool. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 19/08/2026

Short vid: Spotlight on a spot diagnosis: scabies. instagram.com/mariocaldararomd tiktok.com/@mariocaldararomd youtube.com/@MarioCaldararoMD facebook.com/pathognomonicsignsofdisease

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 19/08/2026

Hutchinson's sign history. Hutchinson first described his "melanotic whitlow" in 1886, and it was called "Hutchinson's melanotic whitlow" until 1981, when the American dermatologist Alfred Kopf (who gave us the ABCDs of melanoma) first wrote it as "Hutchinson's sign." #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 18/08/2026

The blue-dot sign. A small, tender, blue to blue-black discoloration visible through the scrotal skin, usually at the upper pole of the testis. Classically held to mean torsion of one of the testicular appendages. But is it really pathognomonic, or overstated? #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 17/08/2026

Latest short video examining the pathognomonic claim of dendritic keratitis. instagram.com/mariocaldararomd tiktok.com/@mariocaldararomd youtube.com/@MarioCaldararoMD facebook.com/pathognomonicsignsofdisease #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 17/08/2026

Are Achilles Tendon Xanthomas really pathognomonic for autosomal dominant familial hypercholesterolemia? Not strictly. Also seen in cerebrotendinous xanthomatosis and sitosterolemia. Both rare. Definitely best for the test and real in the field. #pathognomonic #meded"

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 14/08/2026

The lead pipe sign classically points to chronic ulcerative colitis, but the "ahaustral colon" also be seen in broader IBD, systemic sclerosis, chronic Salmonella, tuberculosis, rare amebiasis, and chronic stimulant laxative use. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 13/08/2026

What is the mechanism of Russell’s sign? . . . Scraping of the knuckles on dorsum of the hand against the incisors during repeated bouts of self-induced vomiting. An important clue to this harmful behavior, and oft-thought to be pathognomonic...but is it? #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 12/08/2026

In 1887 Paget described a disease he called osteitis deformans after observing a number of older men who developed bone deformities, pain, and fractures. Now known as Paget's disease of bone. Fun fact: Occultist Aleister Crowley claimed Paget treated his dad's tongue cancer. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 11/08/2026

Sign Spotlight: the porcelain gallbladder, a curvilinear or rim-like calcification of the gallbladder wall, often making an eggshell outline around the lumen. Think chronic cholecystitis, from repeated inflammatory insults. Pathognomonic? We'll see. #pathognomonic #meded #surgery #gastroenterology

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 10/08/2026

Is the bird’s beak sign really pathognomonic for achalasia? . . . No! Also seen in pseudoachalasia, a secondary type of LES obstruction from some other cause, usually malignancy. But Chagas disease, aortic aneurysm, and infiltrative diseases have also been reported. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 07/08/2026

This is circinate balanitis: circular, inflammatory dermatitis lesions of the glans commonly associated with reactive arthritis, but also seen in Zoon balanitis, candidiasis, contact dermatitis, lichen planus, and rarely carcinoma in situ. #pathognomonic #meded

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 06/08/2026

Why purple abdominal striae in Cushing's syndrome? It's all the effects of chronic hypercortisolism: 1. thinning of the dermis and epidermis making underlying vasculature more visible 2. reduction of collagen turnover 3. increased truncal subcutaneous fat deposition. #pathognomonic #meded"

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 05/08/2026

The genetic basis for Bloom syndrome was not discovered until 1995 when the BLM mutation at the heart of the disease was found, 40 years after the syndrome was first written about and 30 years after its hallmark cytogenetic finding was seen: hyper sister chromatid exchange. #pathognomonic #meded"

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 04/08/2026

Donovan bodies are intracytoplasmic bacterial inclusions seen within macrophages in granuloma inguinale/donovanosis. They've got one of the two main bipolar "safety pin" appearances in microbiology. The other? Yersinia spp. The difference? Intracellular vs. extracellular. #pathognomonic #meded"

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Mario D. Caldararo, MD @mariocaldararomd.bsky.social · 03/08/2026

Are Schiller–Duval Bodies really pathognomonic for Yolk sac tumor? Not strictly. They've been seen in pseudopapillary neoplasm of the pancreas, rectal cancer, and somatic carcinomas that undergo reprogramming toward a pluripotent phenotype. Definitely best for the tst. #pathognomonic #meded"

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