Dermatology

Corn/callus (singular: callus, callosity, tyloma; plural: callosities, tylomas, tylomata) Clavus (clavi; singular: clavus, corn, heloma; plural: corns, helomas, helomata)

Are You Confident of the Diagnosis?

Characteristic findings on physical examination

Corns (clavi) are very well demarcated and usually are less than 1.5cm in diameter (Figure 1, Figure 2). Clavi may be further classified as a hard clavus (heloma durum) or a soft clavus (heloma mole). Calluses are poorly demarcated and can be of any size (Figure 3). Both show exaggerated skin markings and may show hemorrhage, yellow discoloration from old hemorrhage, or hyperpigmentation. Both are due to thickenings and increases in the density of the epidermal stratum corneum along with changes in the deeper layers of the skin: the stratum malpighi and dermis, which are responsible for creating these increases in the thickness, density and chemical composition of the stratum corneum.

Clavus 10x

Figure 2.

Callus (magnification, 20x)

Figure 3.

Callus (magnification, 20x)

Callus shows a markedly dense, usually orthokeratotic stratum corneum underlain by mild acathosis, variable hypergranulosis, and increased collagenization of the superficial dermis. There may be mucin deposition in the dermis, hemorrhage around blood vessels, streaking of collagen on the sides of the dermal papillae.

Corns show a very dense collagen plug surrounded by epidermis with the changes noted above. In addition, the dermal papillae may be angled toward or away from the center of the lesion. Over the center of the lesion, under the tip of the plug of keratin, the epidermis is often atrophic. Dermal blood vessels are more likely to be damaged than those underlying a callus.

Diagnosis confirmation

The differential diagnosis of a callus is seldom an issue. Treatment may be challenging; diagnosis less commonly so. The most important differential to consider is contact dermatitis, often superimposed on the callus.

The key differential diagnosis of a clavus is a verruca vulgaris, particularly a verruca plantaris. Paring of a callus with a small knife the surface downward eventually reveals small dark spots when dealing with a verruca, corresponding to the thrombosed blood vessels seen histologically. These spots are not seen when paring a clavus. It is important to make this differential because the treatment for these two entities is very different.

Who is at Risk for Developing this Disease?

Corns and calluses are extremely common and affect most of the population at one time or another.

What is the Cause of the Disease?

Etiology

Pathophysiology

Calluses are due to lateral pressure combined with downward pressure on the skin, producing a reaction. If the process is too acute and severe, it exceeds the capacity of the skin to react and produces instead a blister, known as a “friciton blister.” If the pressure is merely lateral, as in rubbing a puritic site, the result instead is lichen simplex chronicus, seen clinically as increased skin markings (ie, increased prominences of the lines that can be seen with the naked eye demarcating diamond-shaped skin zones about 2 mm in diameter) and microscopically as thickening of all the layers of the skin above the reticular dermis.

If there is direct injury to the underlying dermis, the result is a scar (cicatrix), consisting of fibrotic connective tissue changes in the dermis. Indirect injury to the dermis, such as that caused by the downward pressure that caused the callus, may produce mucin deposition in the dermis.

Calluses occur in numerous sites depending on pressure exerted on that site. They often serve a useful purpose, as calluses on the palms of a manual laborer or on the soles of a worker who must chronically walk over difficult terrain (eg, partially crushed seashells) without shoes. Some calluses may therefore be classified as physiologic. Such calluses may also cause pain and dysfunction, however, depending on the exact site, size and shape. Calluses in specific sites often have vernacular names as noted in Table I .

Table I.

Vernacular names of calluses
Vernacular Term Location Association / Cause
Cameo engraver's corn Thumb and digits Due to repeated use of micro-engraving tools
Cherry picker's thumb Thumb and digits Due to repeated use of cherry picking tools
Cigarette lighter's thumb Thumb, radial aspect Due to repeated cigarette lighter flicking
Crew member (rower's callus) Palmar metacarpophalangeal surfaces Due to friction while rowing
Hairdresser's hand First finger on dominant hand Due to friction caused by the handle of scissors
Jeweler's callus Thumb and digits Due to repeated use of jeweler's tools
Knuckle pads Knuckles Boxing*
Prayer's callus Brow Due to kneeling with weight pressed onto brow
Russell's sign** Dorsum of either hand over metacarpophalangeal and interphalangeal joints Due to friction involved in self-induced emesis in bulimia nervosa
Screwdriver operator's callus Palm Due to improperly held screw driver
Spine bumps Skin overlying spinal column Due to spinning on the back during dancing
Sucking callus Lip, hand or foot of a young infant Due to sucking affected site by young infant
Vamp's disease Foot Due to tight heeled shoes
Violinist's neck Lateral cervical region (neck) Due to holding violin with base on affected area
Weight lifter's callus Palmar metacarpophangeal surfaces Due to friction while lifting weights

In contrast, a clavus is a focal lesion caused by a focal influence. An example is a nail in ones shoe extending above the sole. Clavi are almost always pathological, causing pain rather than easing it. Hard clavi are common, often seen on the sole of the foot. Soft clavi are seen on more moist areas, such as between the toes. Podiatrists have termed this lesion “porokeratosis” for many decades, and thus are protected in that usage. “Porokeratosis,” of course, has a very different meaning in dermatology, where it denotes a possibly precancerous condition.

Systemic Implications and Complications

Diabetes mellitus may lead to either process due to loss of sensation in the lower limbs; in many cases the patient is unaware of even grossly apparent lesions. Diabetic patients are more prone to infectious complications and friction blisters.

Treatment Options

1. Removal of mechanical stress, eg, properly fitting shoes, moleskin, cut-out foam adhesive pads, diabetic socks

2. Keratolytics

- 40% salicylic acid pads and plaster

- 40% urea cream

- 12% lactic acid cream

Patients with peripheral neuropathies should avoid using keratolytics.

Optimal Therapeutic Approach for this Disease

Lesions are managed primarily by removing the mechanical stress that caused the lesion and by appropriate use of keratolytics when necessary. Special care must be taken to be sure the patient does not have diabetes mellitus or peripheral vascular disease in the relevant area.

When calluses are desirable, as in ceratin training situations, their development may be accelerated by applying a protein cross-linker, such as formalin, topically to the area.

Patient Management

Prognosis is excellent if proper management is instituted and followed. If the patient has diabetes mellitus or peripheral vascular disease in the relevant area, however, ulceration and infection, with a difficult course, may follow. If an ulcer appears, it may be difficult to treat. The clinician cannot exclude other causes of an ulcer, however, such as verrucous carcinoma, so care must be taken to ensure proper management should an ulcer appear.

Unusual Clinical Scenarios to Consider in Patient Management

Inevitably, newer “forms” of calluses will be desribed dependent upon where pressure has been applied. For example, sitting cross-legged was recently reported as an etiology.

What is the Evidence?

Shahk, R, Tiwari, RR. "Occupational skin problems in construction workers". Indian J Dermatol. . vol. 55. 2010. pp. 348-51.

(This is an excellent analysis of skin problems of construction workers at a site in India. They mainly consist of calluses and contact dermatitis.)

Tautisinwat, N, Janchai, S. "Common foot problems in a diabetic foot clinic". J Med Assoc Thai . vol. 91. 2008. pp. 1097-101.

(This is an excellent anaylsis of diabetic foot problems in a clinic devoted exclusively to these patients.)
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