A pathognomonic sign is one so characteristic of a condition that, on its own, it effectively points to the diagnosis. In practice, very few signs are strictly pathognomonic, and most of the classic ones are better described as highly suggestive. Either way, recognising them instantly is high-yield for exams and for safe practice. Here is a reference table of the classic signs worth knowing and the condition each points to.
Key takeaways
- A truly pathognomonic sign effectively confirms a diagnosis on its own, but few signs are this specific.
- Most classic signs are strongly suggestive rather than strictly pathognomonic, so confirm where needed.
- Recognising these signs fast is high-yield for UKMLA, PLAB, MRCP and MRCGP.
- Use the sign as a prompt to the diagnosis, then check it fits the rest of the picture.
- Build these into your illness scripts so recognition becomes automatic.
What does pathognomonic mean?
Pathognomonic means a finding is so specific to one condition that its presence essentially establishes the diagnosis. The honest caveat worth holding onto is that genuine pathognomonic signs are rare. Many of the signs taught as pathognomonic, such as a malar rash, are in fact strongly suggestive but not exclusive. The practical approach is to treat a classic sign as a strong prompt towards a diagnosis, then confirm it against the rest of the presentation rather than stopping there.
Pathognomonic and classic signs reference table
| Sign | Points to | Note |
|---|---|---|
| Koplik spots | Measles | Small white buccal spots, appear before the rash |
| Rose spots | Typhoid fever | Faint pink trunk macules |
| Janeway lesions, Osler nodes, Roth spots | Infective endocarditis | Embolic and immune phenomena |
| Gottron papules, heliotrope rash | Dermatomyositis | Knuckle papules and a violaceous eyelid rash |
| Kayser-Fleischer rings | Wilson disease | Copper deposition at the corneal margin |
| Cherry-red spot at the macula | Central retinal artery occlusion | Also seen in some storage diseases |
| Charcot triad (fever, jaundice, right upper quadrant pain) | Ascending cholangitis | Reynolds pentad adds shock and confusion |
| Strawberry tongue | Scarlet fever or Kawasaki disease | Consider the wider picture |
| Slapped-cheek rash | Parvovirus B19 (erythema infectiosum) | Common in children |
| Target (iris) lesions | Erythema multiforme | Often post-infective |
| Auspitz sign | Psoriasis | Pinpoint bleeding when scale is removed |
| Nikolsky sign | Pemphigus, or SJS and toxic epidermal necrolysis | Skin shears with light pressure |
| Tophi | Gout | Urate deposits, often at the ear or joints |
| Heberden and Bouchard nodes | Osteoarthritis | Distal and proximal interphalangeal joints |
| Boutonniere and swan-neck deformities | Rheumatoid arthritis | Chronic joint changes |
| Murphy sign | Acute cholecystitis | Arrest of inspiration on palpation |
| McBurney point tenderness | Appendicitis | Right iliac fossa |
| Cullen and Grey Turner signs | Retroperitoneal haemorrhage, including severe pancreatitis | Periumbilical and flank bruising |
| Chvostek and Trousseau signs | Hypocalcaemia | Facial twitch and carpopedal spasm |
| Brushfield spots | Down syndrome | Iris speckling |
| Lisch nodules, cafe-au-lait macules | Neurofibromatosis type 1 | Iris hamartomas and skin macules |
How to use these signs in revision
A sign is a shortcut to a diagnosis, not a substitute for the rest of the reasoning. Three habits make them stick: link each sign to its condition inside a full illness script, learn the one or two conditions a sign could indicate rather than memorising it in isolation, and practise recognising the sign in case context rather than as a flashcard. For the method behind this, see our spot diagnosis guide and our explainer on illness scripts. To practise recognition in cases, play today's iatroX Rounds.
Frequently asked questions
What is a pathognomonic sign? A finding so specific to one condition that its presence essentially confirms the diagnosis. In reality few signs are strictly pathognomonic, so most classic signs should be treated as strongly suggestive.
Are these signs enough to diagnose a condition? Rarely on their own. Use a classic sign as a strong prompt to a diagnosis, then confirm it against the rest of the history, examination and investigations.
Why learn pathognomonic signs? Because they allow fast recognition, which is high-yield in exams and useful in practice. They are most powerful when built into a full illness script rather than memorised in isolation.
Which signs are genuinely pathognomonic? Very few. Koplik spots in measles are a classic example of a near-pathognomonic sign. Many others, such as a malar rash, are suggestive but not exclusive.
How do I remember them? Link each sign to its condition and the discriminating context, and practise recognising it in cases rather than as a standalone fact. Spaced daily practice consolidates them.