Diabetic infections

Diabetic infections 

Infections cause considerable morbidity and mortality in patients with diabetes mellitus.

Infections may precipitate metabolic derangements, and conversely, the metabolic derangements of diabetes may facilitate infection.

Diabetes increases susceptibility to various types of infections. The most common sites of infection in diabetic patients are the skin and urinary tract.

Mechanism of Infection in diabetes 

Hyperglycemia and acidemia exacerbate impairments in humoral immunity and polymorphonuclear leukocyte and lymphocyte functions but are substantially reversed when pH and blood glucose levels return to normal.

Patients with long-standing diabetes tend to have microvascular and macrovascular disease with resultant poor tissue perfusion and increased risk of infection.

Moreover, the ability of the skin to act as a barrier to infection may be compromised when the diminished sensation of diabetic neuropathy results in unnoticed injury.

Below are the lists of common diabetic associated infections.

Ear, Nose, and Throat Infections(ENT infections)

Malignant otitis externa and rhinocerebral mucormycosis are 2 head-and-neck infections seen almost exclusively in patients with diabetes.

Malignant or necrotizing otitis externa principally occurs in diabetic patients older than 35 years and is almost always due to Pseudomonas aeruginosa. 

Infection starts in the external auditory canal and spreads to adjacent soft tissue, cartilage, and bone. Patients typically present with severe ear pain and otorrhea.

Rhinocerebral mucormycosis, an invasive disease that occurs in patients with poorly controlled diabetes, especially those with diabetic ketoacidosis.

Organisms colonize the nose and paranasal sinuses, spreading to adjacent tissues by invading blood vessels and causing soft tissue necrosis and bony erosion.

Examination of the auditory canal may reveal granulation tissue, but spread of infection to the pinna, preauricular tissue, and mastoid often makes the diagnosis apparent.

Involvement of the cranial nerves, particularly the facial nerve, is common; when infection extends to the meninges, it is often lethal. 

Computed tomography (CT) scanning or magnetic resonance imaging (MRI) helps to define the extent of disease.

Intravenous (IV) antipseudomonal antibiotics should be started immediately in patients with invasive disease.

Diabetic patients with severe otitis externa but no evidence of invasive disease can be treated with an otic antibiotic drop and oral ciprofloxacin with closed follow up.

Rhinocerebral mucormycosis

Rhinocerebral mucormycosis collectively refers to infections caused by various ubiquitous molds. 

Invasive disease occurs in patients with poorly controlled diabetes, especially those with diabetic ketoacidosis.

Organisms colonize the nose and paranasal sinuses, spreading to adjacent tissues by invading blood vessels and causing soft tissue necrosis and bony erosion.

Patients with rhinocerebral mucormycosis usually present with periorbital or perinasal pain, swelling, and induration. Bloody or black nasal discharge may be present.

Involvement of the orbits, with lid swelling, proptosis, and diplopia, is common. 

The nasal turbinates may appear dusky red, ulcerated, or frankly necrotic. 

Black, necrotic nasal mucosal or palatal tissue is an important clue. 

The infection may invade the cranial vault through the cribriform plate, resulting in cerebral abscess, cavernous sinus thrombosis, or internal carotid artery thrombosis.

Wet smears of necrotic tissue often reveal broad hyphae and distinguish mucormycosis from severe facial cellulitis.

Treatment consists of controlling the predisposing hyperglycemia and acidemia, giving IV amphotericin B, and immediate surgical debridement.

 Until the diagnosis is confirmed, antistaphylococcal antibiotic therapy is appropriate.

Skin and Soft Tissue Infections

Sensory neuropathy, atherosclerotic vascular disease, and hyperglycemia all predispose patients with diabetes to skin and soft tissue infections.

These can affect any skin surface but most commonly involve the feet.

Bullosis diabeticorum is a spontaneous, noninflammatory, blistering condition of acral skin that is unique to patients with diabetes mellitus. 

Cellulitis, lymphangitis, and, most ominously, staphylococcal sepsis can complicate even the smallest wound. 

Minor wound infections and cellulitis are typically caused by Staphylococcus aureus or hemolytic streptococci.

Penicillinase-resistant synthetic penicillin or a first-generation cephalosporin has been effective for the outpatient treatment of minor infections.

Necrotizing infections of the skin, subcutaneous tissues, fascia, or muscle can also complicate wounds, particularly cutaneous ulcers. 

These infections are typically polymicrobial, involving group A streptococci, enterococci, S aureus, Enterobacteriaceae, and various anaerobes. 

Surgical debridement is necessary for necrotizing infections. Antibiotic coverage should reflect the range of potential pathogens.

Urinary Tract Infections

Patients with diabetes have an increased risk of asymptomatic bacteriuria and pyuria, cystitis, and, more important, serious upper urinary tract infection.

The treatment of cystitis is essentially the same as that in patients without diabetes, except that longer courses of therapy are generally recommended (eg, 7 days for uncomplicated cystitis).

Individuals with a neurogenic bladder due to diabetic neuropathy may not empty their bladder well and may require urologic referral.

Treatment of pyelonephritis, kidney inflections,  does not differ for patients with diabetes. 

Pyelonephritis makes control of diabetes more difficult by causing insulin resistance; in addition, nausea may limit the patient's ability to maintain normal hydration.

The ensuing hyperglycemia further compromises their immune response. 

Also, patients with diabetes have increased susceptibility to complications of pyelonephritis (eg, renal abscess, emphysematous pyelonephritis, renal papillary necrosis, gram-negative sepsis).

Emphysematous pyelonephritis is an uncommon, necrotizing renal infection caused by Escherichia coli,Klebsiella pneumoniae, or other organisms capable of fermenting glucose to carbon dioxide

The presentation is usually similar to that of uncomplicated pyelonephritis, and the diagnosis is established by identifying renal gas on a plain radiograph, a CT scan, or an ultrasonogram. 

Surgery is indicated after diagnosis.

Osteomyelitis

Contiguous spread of a polymicrobial infection from a skin ulcer (particularly a chronic ulcer) to adjacent bone is common in patients with diabetes.

Cultures from superficial wound swabs often fail to identify the causative organism. Cultures from biopsy or curettage of the debrided ulcer base are preferred. 

If osteomyelitis is apparent on physical examination (eg, if the wounds are deep enough to expose tendons or bone), radiography, or MRI, the patient should be admitted for IV antibiotic treatment. 

Emphysematous Cholecystitis

Cholecystitis, gall bladder infection, is usualy  severe and a  fulminating infection, especially with gas-forming in organisms is more common diabetic patients. 

The diagnosis can be made by finding gas in the gallbladder lumen, wall, or surrounding tissues. 

Perforation is common, and, even with immediate surgery, the rate of mortality is high. 

Infection is typically polymicrobial and Clostridial species are found 

Other infections 

The incidences of staphylococcal and Klebsiella pneumoniae infections are greater in people with diabetes and cryptococcal infections and coccidioidomycoses are more virulent in patients with diabetes.

 Diabetes is a risk factor for reactivation of tuberculosis in any previously exposed or not properly treated  individuals.