Early diagnosis is difficult as the disease often looks early on like a simple superficial skin infection. While a number of laboratory and imaging modalities can raise the suspicion for necrotizing fasciitis, the gold standard for diagnosis is a surgical exploration in the setting of high suspicion. When in doubt, a small "keyhole" incision can be made into the affected tissue, and if a finger easily separates the tissue along the fascial plane, the diagnosis is confirmed and an extensive debridement should be performed.

Computed tomography (CT scan) is able to detect approximately 80% of cases while MRI may pick up slightly more.

The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score can be utilized to risk stratify people having signs of cellulitis to determine the likelihood of necrotizing fasciitis being present. It uses six serologic measures: C-reactive protein, total white blood cell count, hemoglobin, sodium, creatinine and glucose. A score greater than or equal to 6 indicates that necrotizing fasciitis should be seriously considered. The scoring criteria are as follows:

- CRP (mg/L) ≥150: 4 points

- WBC count (×10/mm)

- <15: 0 points

- 15–25: 1 point

- >25: 2 points

- Hemoglobin (g/dL)

- >13.5: 0 points

- 11–13.5: 1 point

- <11: 2 points

- Sodium (mmol/L) <135: 2 points

- Creatinine (umol/L) >141: 2 points

- Glucose (mmol/L) >10: 1 point

As per the derivation study of the LRINEC score, a score of ≥6 is a reasonable cut-off to rule in necrotizing fasciitis, but a LRINEC <6 does not completely rule out the diagnosis. Diagnoses of severe cellulitis or abscess should also be considered due to similar presentations. 10% of patients with necrotizing fasciitis in the original study still had a LRINEC score <6. But a validation study showed that patients with a LRINEC score ≥6 have a higher rate of both mortality and amputation.

The differential diagnosis for heel pain is extensive and includes pathological entities including, but not limited to the following: calcaneal stress fracture, calcaneal bursitis, osteoarthritis, spinal stenosis involving the nerve roots of lumbar spinal nerve 5 (L5) or sacral spinal nerve 1 (S1), calcaneal fat pad syndrome, hypothyroidism, seronegative spondyloparthopathies such as reactive arthritis, ankylosing spondylitis, or rheumatoid arthritis (more likely if pain is present in both heels), plantar fascia rupture, and compression neuropathies such as tarsal tunnel syndrome or impingement of the medial calcaneal nerve.

A determination about a diagnosis of plantar fasciitis can usually be made based on a person's medical history and physical examination. In cases in which the physician suspects fracture, infection, or some other serious underlying condition, an x-ray may be used to make a differential diagnosis. However, and especially for people who stand or walk a lot at work, x-rays should not be used to screen for plantar fasciitis unless imaging is otherwise indicated as using it outside of medical guidelines is unnecessary health care.

Plantar fasciitis is usually diagnosed by a health care provider after consideration of a person's presenting history, risk factors, and clinical examination. Tenderness to palpation along the inner aspect of the heel bone on the sole of the foot may be elicited during the physical examination. The foot may have limited dorsiflexion due to tightness of the calf muscles or the Achilles tendon. Dorsiflexion of the foot may elicit the pain due to stretching of the plantar fascia with this motion. Diagnostic imaging studies are not usually needed to diagnose plantar fasciitis. However, in certain cases a physician may decide imaging studies (such as X-rays, diagnostic ultrasound or MRI) are warranted to rule out serious causes of foot pain.

Other diagnoses that are typically considered include fractures, tumors, or systemic disease if plantar fasciitis pain fails to respond appropriately to conservative medical treatments. Bilateral heel pain or heel pain in the context of a systemic illness may indicate a need for a more in-depth diagnostic investigation. Under these circumstances, diagnostic tests such as a CBC or serological markers of inflammation, infection, or autoimmune disease such as C-reactive protein, erythrocyte sedimentation rate, anti-nuclear antibodies, rheumatoid factor, HLA-B27, uric acid, or Lyme disease antibodies may also be obtained. Neurological deficits may prompt an investigation with electromyography to evaluate for damage to the nerves or muscles.

An incidental finding associated with this condition is a heel spur, a small bony calcification on the calcaneus (heel bone), which can be found in up to 50% of those with plantar fasciitis. In such cases, it is the underlying plantar fasciitis that produces the heel pain, and not the spur itself. The condition is responsible for the creation of the spur though the clinical significance of heel spurs in plantar fasciitis remains unclear.

Other conditions that may mimic cellulitis include deep vein thrombosis, which can be diagnosed with a compression leg ultrasound, and stasis dermatitis, which is inflammation of the skin from poor blood flow. Signs of a more severe infection such as necrotizing fasciitis or gas gangrene that would require prompt surgical intervention include purple bullae, skin sloughing, subcutaneous edema, and systemic toxicity. Misdiagnosis can occur in up to 30% of people with suspected lower-extremity cellulitis, leading to 50,000 to 130,000 unnecessary hospitalization and $195 to $515 million in avoidable healthcare spending annually in the United States.

Associated musculoskeletal findings are sometimes reported. When it occurs with acne conglobata, hidradenitis suppurativa, and pilonidal cysts, the syndrome is referred to as the follicular occlusion triad or tetrad.

Lyme disease can be misdiagnosed as staphylococcal- or streptococcal-induced cellulitis. Because the characteristic bullseye rash does not always appear in people infected with Lyme disease, the similar set of symptoms may be misdiagnosed as cellulitis. Standard treatments for cellulitis are not sufficient for curing Lyme disease. The only way to rule out Lyme disease is with a blood test, which is recommended during warm months in areas where the disease is endemic.

In medicine, fasciitis is an inflammation of the fascia, which is the connective tissue surrounding muscles, blood vessels and nerves.

In particular, it often involves one of the following diseases:

- Necrotizing fasciitis

- Plantar fasciitis

- Eosinophilic fasciitis

- Paraneoplastic fasciitis

In those who have previously had cellulitis, the use of antibiotics may help prevent future episodes. This is recommended by CREST for those who have had more than two episodes.

While recent case series (n=9-80) studies have found a mortality rate of 20-40%, a large (n=1641) 2009 study reported a mortality rate of 7.5%.

The key to diagnosis is skin changes combined with blood eosinophilia but the most accurate test is a skin, fascia and muscle biopsy.

Diagnosis is usually clinical. Smear for fusospirochaetal bacteria and leukocytes; blood picture occasionally. The important differentiation is with acute leukaemia or herpetic stomatitis.

Raised inflammatory markers (high ESR, CRP) are common but nonspecific. Examination of the coughed up mucus is important in any lung infection and often reveals mixed bacterial flora. Transtracheal or transbronchial (via bronchoscopy) aspirates can also be cultured. Fiber optic bronchoscopy is often performed to exclude obstructive lesion; it also helps in bronchial drainage of pus.

Fournier gangrene is usually diagnosed clinically, but laboratory tests and imaging studies are used to confirm diagnosis, determine severity and predict outcomes. X-rays and ultrasounds may show the presence of gas below the surface of the skin. A CT scan can be useful in determining the site of origin and extent of spread.

Diagnosis is made by clinical observation and the following tests.

(1) Gram stain of the fluid from pustules or bullae, and tissue swab.

(2) Blood culture

(3) Urine culture

(4) Skin biopsy

(5) Tissue culture

Magnetic resonance imaging can be done in case of ecthyma gangrenosum of plantar foot to differentiate from necrotizing fasciitis.

Treatment includes irrigation and debridement of necrotic areas (areas of dead and/or dying gum tissue), oral hygiene instruction and the uses of mouth rinses and pain medication. If there is systemic involvement, then oral antibiotics may be given, such as metronidazole. As these diseases are often associated with systemic medical issues, proper management of the systemic disorders is appropriate.

It is often seen as a repetitive stress injury, and thus lifestyle modification is typically the basic course of management strategies. For example, a person should begin doing foot and calf workouts. Strong muscles in the calves and lower legs will help take the stress off the bone and thus help cure or prevent heel spurs. Icing the area is an effective way to get immediate pain relief.

Conventional radiography is usually the initial assessment tool when a calcaneal fracture is suspected. Recommended x-ray views are (a) axial, (b) anteroposterior, (c) oblique and (d) views with dorsiflexion and internal rotation of the foot. However, conventional radiography is limited for visualization of calcaneal anatomy, especially at the subtalar joint. A CT scan is currently the imaging study of choice for evaluating calcaneal injury and has substituted conventional radiography in the classification of calcaneal fractures. Axial and coronal views are obtained for proper visualization of the calcaneus, subtalar, calcaneocuboid and talonavicular joints.

The diagnostic testing for vasculitis should be guided by the patient's history and physical exam. The clinician should ask about the duration, onset, and presence any associated symptoms such as weight loss or fatigue (that would indicate a systemic cause). It is important to distinguish between IgA and non-IgA vasculitis. IgA vasculitis is more likely to present with abdominal pain, bloody urine, and joint pain. In the case that the cause is not obvious, a reasonable initial workup would include a complete blood count, urinalysis, basic metabolic panel, fecal occult blood testing, erythrocyte sedimentation rate (ESR), and C-reactive protein level. Small vessel cutaneous vasculitis is a diagnosis of exclusion and requires ruling out systemic causes of the skin findings. Skin biopsy (punch or excisional) is the most definitive diagnostic test and should be performed with 48 hours of appearance of the vasculitis. A skin biopsy will be able to determine if the clinical findings are truly due to a vasculitis or due to some other cause.

Aside from surgery, there are a few options for handling an accessory navicular bone that has become symptomatic. This includes immobilization, icing, medicating, physical therapy, and orthotic devices. Immobilizing involves placing the foot and ankle in a cast or removable walking boot. This alleviates stressors on the foot and can decrease inflammation. Icing will help reduce swelling and inflammation. Medication involves usage of nonsteroidal anti-inflammatory drugs, or steroids (taken orally or injected) to decrease inflammation. Physical therapy can be prescribed in order to strengthen the muscles and help decrease inflammation. Physical therapy can also help prevent the symptoms from returning. Orthotic devices (arch support devices that fit in a shoe) can help prevent future symptoms. Occasionally, the orthotic device will dig into the edge of the accessory navicular and cause discomfort. For this reason, the orthotic devices made for the patient should be carefully constructed.

Differentiation between this and SCC would be based on a history of recent trauma or dental treatment in the area.

Immunohistochemistry may aid the diagnosis. If the lesion is NS, there will be focal to absent immunoreactivity for p53, low immunoreactivity for MIB1 (Ki-67), and the presence of 4A4/p63- and calponin-positive myoepithelial cells.

The main organism associated with ecthyma gangrenosum is "Pseudomonas aeruginosa". However, multi-bacterial cases are reported as well. Prevention measures include practicing proper hygiene, educating the immunocompromised patients for awareness to avoid possible conditions and seek timely medical treatment.

Diagnosis is by a swab of the affected area for laboratory testing. A Gram stain is performed to show Gram-positive cocci in chains. Then, the organism is cultured on blood agar with an added bacitracin antibiotic disk to show beta-hemolytic colonies and sensitivity (zone of inhibition around the disk) for the antibiotic. Culture on agar not containing blood, and then performing the catalase test should show a negative reaction for all streptococci. "S. pyogenes" is CAMP and hippurate tests negative. Serological identification of the organism involves testing for the presence of group-A-specific polysaccharide in the bacterium's cell wall using the Phadebact test.

The rapid pyrrolidonyl arylamidase (PYR) test is used for the presumptive identification of group A beta-hemolytic streptococci. GBS gives a negative finding on this test.

Common treatments include corticosteroids such as prednisone, though other medications such as hydroxychloroquine have also been used.

The prognosis is usually good in the case of an early treatment if there is no visceral involvement.

Evaluating soft-tissue involvement is the most important aspect of the clinical examination because of its association with patient outcome. Skin blisters may become infected if medical attention is delayed, which can lead to necrotizing fasciitis or osteomyelitis, causing permanent damage to muscle or bone. Ligament and tendon involvement should also be explored. Achilles tendon injury can be seen with posterior (Type C) fractures. Since calcaneal fractures are related to falls from height, other concomitant injuries should be evaluated. Vertebral compression fractures occur in approximately 10% of these patients. A trauma-focused clinical approach should be implemented; tibial, knee, femur, hip, and head injuries should be ruled out by means of history and physical exam.

Manual therapy and exercise have better efficacy in the long term than electrophysical agents and exercise for function, but not for pain. Manual therapy and exercise are preferably focused at stretching the plantar fascia.

Most cases respond to antibiotics and prognosis is usually excellent unless there is a debilitating underlying condition. Mortality from lung abscess alone is around 5% and is improving.