Necrobiosis lipoidica is a rare chronic condition that primarily affects individuals with diabetes and results in collagen degeneration, reduced collagen synthesis, atrophy, and lipid deposits. Necrobiosis lipoidica occurs in about 0.7 % of diabetic patients with ulcers developing in 13–35 % of cases. Of ulcerated necrobiosis lipoidica, 70 % of the patients had diabetes mellitus of which 30 % had type I diabetes and 40 % had type II diabetes; 60 % of the patients suffered from arterial hypertension, obesity, and hypercholesterolemia; and 40 % of the patients suffered from psychiatric disorders such as depression and borderline disorder. Ulcerating necrobiosis lipoidica can be seen as part of a generalized inflammatory reaction similar to the inflammatory reaction already known in the pathophysiology of rheumatoid diseases or psoriasis. In patients with clinical atypical painful ulcerations, necrobiosis lipoidica should be considered as a possible differential diagnosis. Therapists should be aware of associated aspects in patients with ulcerated necrobiosis lipoidica who besides diabetes often suffer from other aspects of a metabolic syndrome with increased cardiovascular risk factors. Therefore, these related comorbidities should also be diagnosed and treated [13]. Lesions generally develop on the pretibial area as small red-brown erythematous markings that gradually enlarge. Lesions may present as single or multiple, clearly demarcated, waxy, yellow-brown plaques with depressed centers, which are associated with granulomatous inflammation and collagen degeneration [14].

Porphyria cutanea tarda (PCT) refers to a group of disorders that can be familial or acquired and which result in a deficiency in the function of the heme synthetic enzyme uroporphyrinogen decarboxylase (UROD) [15]. PCT is essentially an acquired disease, but some individuals have a genetic (autosomal dominant) deficiency of UROD that contributes to the development of PCT. These individuals are referred to as having “familial PCT.” Most individuals with the inherited enzyme deficiency remain latent and never have symptoms. The symptoms of PCT are confined mostly to the skin. Blisters develop on sun-exposed areas of the skin, such as the hands, legs, and face. The skin in these areas may blister or peel after minor trauma. Increased hair growth, as well as darkening and thickening of the skin, may also occur. Liver function abnormalities are common but are usually mild, although they sometimes progress to cirrhosis and even liver cancer. PCT is often associated with hepatitis C infection, which can also cause these liver complications. However, liver tests are generally abnormal even in PCT patients without hepatitis C infection.

Gout is an inflammatory disorder of monosodium urate metabolism, which is characterized by the deposition of urate crystals in the joints and soft tissues. Gout usually presents as an acute attack of synovitis which clears completely in a week or so. As far as the tophaceous deposits are concerned, these are commonly present on the ears, in the tendons, and in the joints specially the knee and elbow. Regarding the local skin affections, gouty tophi mainly cause signs of local skin irritation in the form of pain, swelling, and skin erythema [16].

Calciphylaxis is a rare and potentially grave vasculopathy of the skin and subcutaneous tissue that has a female-to-male ratio of 3:1. This condition occurs as a complication of chronic kidney disease, particularly in diabetics and in secondary hyperparathyroidism associated with abnormal calcium metabolism. Calciphylaxis occurs in 1 % of patients with chronic kidney disease and in 4 % of individuals on dialysis [17]. Calciphylaxis initially manifests as irregular livedo reticularis with subcutaneous nodules and plaques. Ultimately, markedly painful, large, necrotic ulcerations ensue. The lower extremities are most commonly involved, although the upper extremities, abdomen, and buttocks can also be affected. Unusual sites of calciphylaxis include the penis, breasts, and neck. The distal pulses may be palpable in the absence of severe peripheral artery disease. Elevated parathyroid hormone and hyperphosphatemia are the most common laboratory abnormalities. Therapy is often ineffective yet controlling hypercalcemia, hyperphosphatemia, and hyperparathyroidism is recommended. Methods for controlling the calcium × phosphate product include eliminating vitamin D analogs, reducing calcium in the dialysis bath, decreasing dietary phosphate and calcium, and substituting sevelamer hydrochloride for calcium-based phosphate binders. Although parathyroidectomy is often recommended, its value remains controversial [18].

Calcinosis cutis is a disorder whereby calcium and phosphorous salts are deposited in the dermis. Leg ulcers are generally asymptomatic but may be tender and present with numerous, dense, pale dermal papules, plaques, nodules, or subcutaneous nodules. The lesions may also be enclosed by a yellowish/whitish gritty substance that ulcerates. Lesions over joints can restrict mobility, while vascular calcification may cause diminished pulses and, in severe cases, cutaneous gangrene [19].

Hansen’s disease (leprosy) is caused by the Mycobacterium leprae organism that predominantly affects the skin and peripheral nerves. Approximately 30 % of people with Hansen’s disease will develop nerve damage that results in peripheral nerve sensory loss, usually in the hands, feet, and eyes. Skin damage can present as thickened, cracked skin that becomes infected and ulcerates. Additional skin changes may include erythematous changes (papules and nodules) or hypopigmented plaques and alopecia [20]. Ulcers in patients with leprosy sequelae remain a major source of economic and social losses, even many years after they have been cured of M. leprae infection. Management of chronic ulcers in patients with leprosy includes different types of dressings, orthopedic and plastic surgeries, plaster casts, special footwear, splints, crutches, wheelchair use, and absolute rest. Despite this, clinical experience shows that patient compliance to the therapeutic procedures is a key consideration in treatment choice and that without patient collaboration the result of the treatment can be frustrating. Low patient adherence to rehabilitation and prevention of disabilities programs (e.g., usage of appropriate footwear) indicates that more research and educational measures are necessary to improve the adoption of such strategies. Ulcers in patients with leprosy can remain for several years after the initial infection is resolved and can result in large economic and social losses. Such losses were observed in this study, which was primarily composed of former patients that have lived with their ulcers for many years. The most important causal factor for neuropathic foot ulcers is the presence of a dynamic or static deformity leading to local areas of peak pressure on insensitive skin, which has been well illustrated by pressure studies. This repetitive overload on specific areas of the sole could partially explain why plantar ulcers are deeper and smaller than leg and ankle ulcers. The free distribution of special footwear does not ensure its adequate utilization. Healthcare workers need to be constantly pushed to establish a patient continuum education process about self-care routines and to improve the techniques currently employed to encourage the use of preventive tools. Low adherence to such programs and self-care procedures is a concern of countries that still bear a significant leprosy burden [21]. The involvement of the peripheral nerves can lead to loss of sensation particularly affecting the hands and lower limbs. As in diabetes, the loss of sensation results in people not being aware of any cuts or burns that they may sustain. For this reason, people with leprosy are more prone to developing hand and lower limb injuries, which may develop into nonhealing ulcers. Leprosy always needs to be considered in the presentation of a nonhealing ulcer, especially in the indigenous population or those from countries where leprosy is noted by the World Health Organization to still occur at higher levels.