Differential Diagnosis
- Single most likely diagnosis
- Cellulitis: The presence of erythema, warmth, and tenderness in both the left external ear and the left leg, particularly over the tibia, suggests an infectious or inflammatory process. Cellulitis is a common condition characterized by these symptoms, and its diagnosis is often clinical.
- Other Likely diagnoses
- Erythema nodosum: This condition could explain the painful erythema and tenderness over the tibia, although it typically presents with more distinct nodules.
- Superficial thrombophlebitis: The tenderness and warmth, especially with flexion of the foot, could suggest a superficial venous thrombosis, although this would typically be associated with more pronounced swelling and possibly a palpable cord.
- Perichondritis (of the ear): Given the involvement of the external ear, perichondritis is a consideration, especially if the cartilage is involved, but the normal TM and EACs make this less likely as a sole diagnosis.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Necrotizing fasciitis: Although less common, this condition presents with similar symptoms of erythema, warmth, and tenderness but is much more severe and can rapidly progress to life-threatening complications. The absence of significant swelling and the equal leg circumference might make this less likely, but it cannot be ruled out without close observation and possibly further diagnostic tests.
- Osteomyelitis: Particularly given the tenderness over the tibia, osteomyelitis (infection of the bone) is a serious condition that could present similarly and requires prompt diagnosis and treatment to prevent long-term damage.
- Deep vein thrombosis (DVT): While the equal leg circumference and the specific location of tenderness might make DVT less likely, it is a critical diagnosis not to miss due to the risk of pulmonary embolism. The presence of tenderness with flexion of the foot (Homan's sign) is a classic but non-specific sign of DVT.
- Rare diagnoses
- Erythema migrans (Lyme disease): If the patient is in an endemic area and has been exposed to ticks, Lyme disease could be a consideration, although the lack of a distinctive "bull's-eye" rash and the involvement of the ear make this less likely.
- Sarcoidosis: This systemic disease can cause skin lesions and could potentially explain the findings, but it would be an unusual presentation without other systemic symptoms or findings.