Ans. a. Diphtheria (Ref: Harrison 19/e p978, 18/e p1189-1190)Bull-neck is seen in severe cases of diphtheria.Respiratory DiphtheriaClinical Features:The clinical diagnosis of diphtheria is based on:Constellation of sore throatQAdherent tonsillar, pharyngeal, or nasal pseudomembranous lesionsQLow-grade feverQOccasionally, weakness, dysphagia, headache, and voice change are the initial manifestationsQ.Neck edema and difficulty breathing are seen in more advanced cases and carry a poor prognosisQ.The systemic manifestations of diphtheria stem from the effects of diphtheria toxin and include weakness as a result of neurotoxicity and cardiac arrhythmias or congestive heart failure due to myocarditisQ.The pseudomembranous lesion is most often located in the tonsiilopharyngeal regionQ.The diphtheritic pseudomembrane is gray or whitish and sharply demarcatedQ.Pseudomembrane in diphtheria is tightly adherent to the underlying tissuesQ.Less commonly, the lesions are detected in the larynx, nares. and trachea or bronchial passages.Large pseudomembranes are associated with severe disease and a poor prognosisQ.A few patients develop swelling of the tonsils and present with "bull-neck" diphtheria, which results from massive edema of the submandibular and paratracheal region and is further characterized by foul breath, thick speech, and stridorous breathingQ.Unlike the exudative lesion associated with streptococcal pharyngitis, the pseudomembrane in diphtheria is tightly adherent to the underlying tissuesQ.Diagnosis:Attempts to dislodge the membrane may cause bleeding.Hoarsensess suggests laryngeal diphtheria, in which laryngoscopy may be diagnostically helpful.In addition, diagnosis requires the isolation of C. diphtheria or the histopathologic isolation of compatible grampositive organismsQ.