Tuberculosis RIPE
Rifampin (orange secretions, CYP inducer), Isoniazid (peripheral neuropathy - give B6, hepatitis), Pyrazinamide (hyperuricemia/gout), Ethambutol (optic neuritis).
Endemic Mycoses Triad
Histoplasma: Ohio/Mississippi River, bird/bat guano, intracellular macrophages. Coccidioides: SW desert, spherules with endospores. Blastomyces: broad-based budding, Great Lakes/East.
Lyme Disease Stages
Stage 1: Erythema migrans; Stage 2: AV block, bilateral Bell palsy; Stage 3: migratory polyarthritis, acrodermatitis chronica. Rx: Doxycycline (Ceftriaxone if carditis/CNS).
Syphilis Diagnosis
Primary: painless chancre. Secondary: maculopapular rash on palms/soles, condyloma lata. Tertiary: gummas, tabes dorsalis, Argyll Robertson pupil. Screen VDRL/RPR, confirm FTA-ABS.
Endemic Dimorphic Fungi Master Comparison
| Fungal Organism | Geographic Endemic Region & Exposure | Diagnostic Microscopic Morphology | Clinical Features & Extrapulmonary Spread |
|---|---|---|---|
| Histoplasma capsulatum | Ohio & Mississippi River Valleys; bat or bird droppings (spelunking, chicken coops) | Small oval yeast (2–4 μm) intracellular inside macrophages; smaller than RBC | Hepatosplenomegaly, tongue/palatal ulcers, pancytopenia; urine/serum Histoplasma antigen |
| Coccidioides immitis / posadasii | Southwestern United States (San Joaquin Valley, Arizona, Southern California); desert sand dust | Large thick-walled spherules (20–60 μm) packed with endospores; much larger than RBC | Valley Fever: Erythema nodosum, arthralgias ('desert rheumatism'), cavitary thin-walled pulmonary lesions, chronic meningitis |
| Blastomyces dermatitidis | Great Lakes, Ohio/Mississippi River, Southeastern US; decaying organic vegetation/wood | Large yeast with broad-based budding and thick double-contoured refractile wall; size equal to RBC | Verrucous / ulcerated skin lesions mimicking squamous cell carcinoma, osteolytic bone lesions, prostate involvement |
| Sporothrix schenckii | Worldwide; rose thorns, sphagnum moss, bark, hay (occupational: gardeners, florists) | Dimorphic; cigar-shaped budding yeast at 37°C; rosettes of conidia at 25°C | Lymphocutaneous sporotrichosis: Painless nodule at prick site that ulcerates with ascending lymphangitic nodules along lymphatic channels; Rx: Itraconazole |
Tick-Borne Zoonoses & Spirochetal Infections
| Infection & Vector | Etiologic Agent | Pathognomonic Clinical Manifestations | Treatment Regimen |
|---|---|---|---|
| Lyme Disease (Ixodes scapularis tick) | Borrelia burgdorferi (spirochete) | Early localized: Erythema migrans ('bull's eye'); Early disseminated: Bilateral facial nerve (Bell) palsy, AV conduction block; Late: Asymmetric mono/oligoarthritis (knee) | Oral Doxycycline (even in children for short courses); IV Ceftriaxone for Lyme carditis (AV block) or neuroborreliosis |
| Rocky Mountain Spotted Fever (RMSF) (Dermacentor tick) | Rickettsia rickettsii (obligate intracellular) | High fever, severe headache, myalgias, and a blanching macular rash that begins on wrists and ankles and spreads centripetally to trunk, palms, and soles | Immediate Doxycycline (do not wait for serologic confirmation; delay carries high mortality from endothelial damage) |
| Syphilis (Sexual transmission / transplacental) | Treponema pallidum (spirochete) | Primary: Painless chancre with clean base; Secondary: Diffuse maculopapular rash on palms and soles, condylomata lata; Tertiary: Argyll Robertson pupils (accommodate but do not react to light), tabes dorsalis, thoracic aortic aneurysm | Early syphilis: Benzathine Penicillin G 2.4 million units IM single dose; Neurosyphilis: IV aqueous crystalline penicillin G; Jarisch-Herxheimer reaction common |
OMM Board Correlate: Cranial & Facial Reflexes in Lyme Facial Palsy
- Stylomastoid Foramen & CN VII: Facial nerve exits temporal bone via the stylomastoid foramen. In Lyme-associated bilateral Bell palsy, temporal bone internal rotation compresses CN VII; temporal rocking and sphenobasilar decompression relieve nerve entrapment.
- Chapman Points: Tonsils and pharynx Chapman point is located at the 1st intercostal space adjacent to the sternum; ear Chapman point is on the superior clavicle lateral to where the subclavius crosses.
Board Traps & Common Distractors
- In patients initiated on Penicillin for secondary syphilis, monitor for the Jarisch-Herxheimer reaction: acute self-limited fever, chills, tachycardia, and vasodilation within hours caused by massive endotoxin-like pyrogen release from dying treponemes; manage supportively with NSAIDs.
- Isoniazid induces functional Pyridoxine (Vitamin B6) deficiency by inhibiting pyridoxine phosphokinase, causing sensory peripheral neuropathy; ALWAYS co-prescribe oral Pyridoxine 25–50 mg daily.
- Ethambutol is notorious for optic neuritis presenting as decreased visual acuity and loss of red-green color discrimination; periodic Snellen and Ishihara chart testing is mandatory.