Lymphadenitis and lymphangitis

Cellulitis is a nonpurulent, spreading infection of the deep dermis and subcutaneous fat, usually caused by beta-hemolytic streptococci, diagnosed clinically and treated with antibiotics alone since there is no collection to drain.

Erysipelas is a superficial bacterial skin infection with prominent dermal lymphatic involvement, almost always caused by group A Streptococcus, producing a painful, sharply demarcated, raised, indurated plaque with a peau d'orange surface. Diagnosis is clinical from the border and depth of involvement, and first-line treatment is oral cephalexin, with intravenous cefazolin for systemic signs and long-term penicillin V for confirmed recurrence.

Necrotizing fasciitis is a rapidly progressive, life-threatening infection of the subcutaneous tissue and superficial fascia driven by vessel thrombosis and bacterial exotoxin production. The hallmark is pain out of proportion to visible skin findings, with crepitus, bullae, and woody induration in advanced disease. Diagnosis is confirmed by direct surgical exploration; the LRINEC score aids risk stratification. Treatment is emergent surgical debridement combined with broad-spectrum empiric antibiotics.

A skin abscess is a purulent, fluctuant collection within the dermis and subcutaneous fat, usually caused by Staphylococcus aureus including MRSA, whose primary treatment is incision and drainage, with antibiotics reserved as an adjunct by size and systemic signs.

Bartonella henselae, acquired from cat scratches or bites, most often causes cat-scratch disease, a clinical diagnosis of an inoculation papule with tender regional lymphadenopathy that is usually self-limited but is treated with azithromycin to speed resolution, while disseminated, ocular, hepatosplenic, or immunocompromised disease needs doxycycline or azithromycin plus rifampin.

Nontuberculous mycobacterial (NTM) lung disease is chronic pulmonary infection with environmental mycobacteria other than the tuberculosis complex, most often Mycobacterium avium complex (MAC). Diagnosis requires clinical, radiologic, and microbiologic criteria together, not culture positivity alone. First-line therapy for MAC is a macrolide plus a rifamycin plus ethambutol, continued until cultures are negative for 12 months.

Tuberculosis, caused by Mycobacterium tuberculosis, remains a leading global cause of infectious death and presents as latent infection, primary/secondary pulmonary disease, or extrapulmonary and disseminated (miliary) disease. Diagnosis rests on AFB smear, NAAT, and mycobacterial culture (the gold standard), and drug-susceptible active disease is treated with a four-drug regimen (isoniazid, rifampin, pyrazinamide, ethambutol) for 2 months followed by isoniazid plus rifampin for 4 to 7 months.

Sporotrichosis is a subacute fungal infection caused by direct cutaneous inoculation of the dimorphic fungus Sporothrix schenckii, classically from a rose thorn or plant matter, producing a nodular ulcer that spreads along lymphatic channels; diagnosis requires culture of the organism, and itraconazole is first-line treatment for cutaneous and lymphocutaneous disease.

Infectious mononucleosis is a systemic illness caused mainly by Epstein-Barr virus, presenting with fever, pharyngitis, and lymphadenopathy, confirmed by heterophile antibody or EBV-specific serology, and managed supportively with contact-sport restriction to prevent splenic rupture.

Hodgkin lymphoma is a B-cell malignancy defined by Reed-Sternberg cells that classically presents with painless, contiguously spreading cervical or mediastinal lymphadenopathy in a young adult, and it is confirmed by excisional lymph node biopsy. Ann Arbor/Lugano stage and interim PET response drive risk-adapted ABVD chemotherapy with or without radiation, and most patients are cured.

Suppurative (septic) thrombophlebitis is an infected venous thrombus with intraluminal bacteria and bacteremia, arising in peripheral IV catheters, central lines, pelvic veins, or the internal jugular vein (Lemierre syndrome). Management centers on source control (catheter removal or vein excision), prolonged antimicrobial therapy, and selective anticoagulation.

Lymphedema is chronic tissue swelling from impaired lymphatic drainage, primary (developmental) or secondary (from surgery, radiation, infection, or malignancy). It causes progressive non-pitting edema that involves the toes, and management is decongestive therapy with compression, skin care, and cellulitis prevention, since there is no curative drug.

Animal and human bites are contaminated wounds whose organism profile depends on the biter, Pasteurella multocida from cats and dogs, Eikenella corrodens and group A Streptococcus from humans, and every wound needs irrigation plus an independent assessment for rabies and tetanus risk. First-line prophylaxis or treatment is amoxicillin-clavulanate 875/125 mg PO every 12 hours, with human and cat bites carrying the highest infection risk and any hand or joint-adjacent wound treated as high risk for septic arthritis or osteomyelitis.

Staphylococcal toxic shock syndrome is a multisystem, toxin-mediated illness caused by TSST-1-producing Staphylococcus aureus acting as a superantigen, classically linked to prolonged tampon use, nasal packing, or a focal staphylococcal infection, diagnosed by a clinical case definition of fever, hypotension, diffuse desquamating rash, and involvement of three or more organ systems, and treated with source control plus antistaphylococcal antibiotics including clindamycin.