​Differential diagnosis of salmonella gastroenteritis 
-appendicitis 
-inflammatoy bowel disease
-amebic dysentery 
-Campylobacter infection 
- Shingellosis 
-food poisoning due to Staphylococcus aureus 
-viral gastroenteritis 

​Differential diagnosis of salivary gland tumor 
-metastatic submandibular lymph node 
-lymphadenopathy from conjunctivitis, otitis media or sinusitis 
-sialolithiasis / salivary gland calculi 
-sialadenitis 

​Differential diagnosis of salicylates poisoning 
-acetaminophen poisoning 
-carbon monoxide poisoning 
-alcoholic ketoacidosis 
-methoanol toxicity 
-ethylene glycol toxicity 

​Differential diagnosis of Sacroiliitis 
-ochronosis 
-lumbar disk herniation 
-facet joint degenerative arthritis 
-synovitis –acne –pustulosis – hyperostosis osteitis syndrome
-diffuse idiopathic skeletal hyperostosis in elderly 
-inflammatory bowel disease 
-osyeitis condensans 

​Differential diagnosis of S4 heart sound 
-cardiomyopathy 
-aortic stenosis 
-coronary artery disease
-hypertensive 
-normal in athelete 

​Differential diagnosis of S3 heart sound
-volume overload
-heart failure 
-normal in young and pregnant 

​Differential diagnosis of Rubella / German Measles 
-congenital herpes simplex virus 
-syphilis 
-toxoplasmosis 
-cytomegalovirus 
-drug eruption 
-Rocky Mountain Spotted Fever 
-polyarthritis due to other causes such as reactive arthritis, parvovirus B19, post rubella vaccination 
-infectious mononucleosis 
-other viral exanthema such as measles, erythema infectiosum ( slapped cheek disease), exanthema subitum( roseola) or primary HIV infection 

​Differential diagnosis of Rosacea 
-dermatomyositis 
-carcinoid 
-systemic lupus erythematosus 
-perioral dermatitis 
-topical steroid use 
-seborrheic dermatitis 
-acne vulgaris 

​Differential diagnosis of Rocky Mountain Spotted Fever 
-scrub typhus, epidemic typhus, endemic typhus, 
-Q fever 
-ehrlichiosis 
-measles 
-viral exanthema 
-influenza 
-typhoid fever 
-bacterial endocarditis 
-secondary syphilis 
-gonococcemia 
-meningococcemia 

​Differential diagnosis of causes of Rickettsial Diseases
-ehrlichiosis 
-Q fever 
-spotted fever group such as Rocky Mountain spotted fever, rickettsial pox, RMSF like, Boutonneuse fever, kenya tick typhus, South African tick fever, Indian tick typhus, Queensland tick typhus, North Asian tick typhus, 
-typhus group such as epidemic typhus, scrub typhus, endemic typhus, California flea rickettsiosis