Callus Differential Diagnosis: A Comprehensive Guide for Accurate Identification

Calluses and corns, both categorized as callosities, are common skin lesions resulting from repetitive mechanical stress, such as friction and pressure. While often used interchangeably in general conversation, in clinical practice, particularly within automotive repair where technicians frequently encounter hand and foot issues due to prolonged standing and physical labor, distinguishing between a callus and other similar-looking skin conditions is crucial for effective management and advice. This article provides a comprehensive guide to the differential diagnosis of calluses, emphasizing the key features that differentiate them from corns, plantar warts, and other dermatological conditions. Understanding these distinctions ensures accurate identification and appropriate recommendations for automotive professionals and anyone experiencing these common foot and hand problems.

Understanding Calluses and Corns: Key Distinctions

Calluses and corns are both hyperkeratotic lesions, meaning they involve a thickening of the stratum corneum, the outermost layer of the epidermis. This thickening is a protective response to repeated friction, pressure, or irritation. However, several key features differentiate these two conditions:

Calluses (Callosity or Tyloma):

• Diffuse and Broad: Calluses are characterized by a more widespread, less defined area of thickened skin. They typically develop over a larger surface area.
• Location: Commonly found on weight-bearing areas like the soles of the feet (especially the heels and balls of the feet), palms of the hands, and knees – areas subjected to frequent pressure or friction. In automotive repair, calluses are often seen on hands due to tool use and pressure points on feet from standing on concrete floors.
• Shape and Borders: They lack a well-defined border and tend to blend gradually into the surrounding skin.
• Sensitivity: Generally less sensitive to direct pressure compared to corns, often described as firm and rubbery.
• Symptoms: Primarily asymptomatic, providing protection. Pain may occur if the callus becomes excessively thick or fissured.

Corns (Clavus, Heloma, Focal Intractable Plantar Hyperkeratosis):

• Focal and Concentrated: Corns are smaller, more focused areas of hyperkeratosis with a dense core. They are sharply demarcated from the surrounding skin.
• Location: Frequently develop on non-weight-bearing areas or areas of intermittent pressure, such as the dorsal surface of toes (especially the little toe), between toes (soft corns), and sometimes on the soles. In automotive technicians, corns can develop from ill-fitting work boots or repetitive pressure points.
• Shape and Borders: Corns have a distinct, often conical or circular shape with a hard, dense core that penetrates deeper into the skin.
• Sensitivity: Characteristically painful, especially with direct pressure. The core of the corn can press on nerve endings, causing sharp pain.
• Types: Classified as hard corns (heloma durum), soft corns (heloma molle), and seed corns, based on their location and consistency.

Figure: Plantar corn, a focal hyperkeratotic lesion that needs to be differentiated from callus and other foot conditions.

Understanding these fundamental differences is the first step in the Callus Differential Diagnosis process. While calluses are generally a broader protective response, corns are more localized and often more symptomatic.

Differential Diagnosis: Distinguishing Calluses from Other Conditions

While the distinction between calluses and corns is important, the differential diagnosis extends to other skin lesions that may mimic calluses. Accurate differentiation is crucial to rule out more serious conditions and implement appropriate management strategies. Key conditions to consider in the differential diagnosis of calluses include:

1. Plantar Warts (Verrucae Plantares) vs. Calluses

Plantar warts are caused by the human papillomavirus (HPV) and are viral infections of the skin. They can often be mistaken for calluses due to their location on the soles of the feet and their thickened, rough texture. However, several features help differentiate plantar warts from calluses:

• Etiology: Calluses are mechanical in origin (pressure/friction), while plantar warts are viral infections.
• Pain: Plantar warts are typically painful with direct pressure and pinching from the sides, whereas calluses are usually painful only with direct pressure.
• Appearance:
  • Plantar Warts: Interrupt normal skin lines, contain thrombosed capillaries that appear as black dots when the surface is pared (Auspitz’s sign is absent after paring corns). They are often rough, cauliflower-like in texture and may have multiple lesions clustered together (mosaic warts).
  • Calluses: Preserve normal skin lines running through them. They have a smooth, uniform texture without black dots.
• Bleeding: Paring a plantar wart often results in pinpoint bleeding due to the disruption of capillaries, which is not typical when paring a callus.
• Dermoscopy: Dermoscopy of plantar warts may reveal thrombosed capillaries (black dots) and a lack of skin lines, while calluses show hyperkeratosis without vascular structures and preserved skin lines.

2. Corns vs. Calluses (Reiterating Key Differences in Differential Diagnosis Context)

While previously discussed, when considering differential diagnosis, it’s vital to reiterate the differentiating points between corns and calluses, as they are both callosities but require different management approaches in some cases:

• Size and Demarcation: Corns are smaller and well-defined, whereas calluses are larger and more diffuse.
• Core: Corns possess a central, dense core that can be enucleated, calluses lack this distinct core.
• Pain with Pressure: Corns are characteristically painful with direct pressure due to the core pressing on nerves. Calluses are generally less sensitive unless very thick.
• Location: Corns typically occur in areas of focused pressure, often on toes, while calluses develop on broader weight-bearing surfaces.

3. Other Conditions in the Differential Diagnosis

Beyond plantar warts and corns, other less common conditions should be considered in the differential diagnosis of calluses, particularly when the presentation is atypical or unresponsive to standard callus treatments:

• Poroma: A benign tumor of the sweat duct, can sometimes mimic a callus. Poromas are usually solitary, flesh-colored to reddish nodules, and may bleed easily when traumatized. Histopathology is often required for definitive diagnosis.
• Warty Dyskeratoma (Isolated Dyskeratosis Follicularis): A rare benign skin tumor that can present as a solitary, wart-like or corn-like lesion. Histopathology is needed for differentiation.
• Calcinosis Cutis: Characterized by calcium deposits in the skin. It can present as firm, whitish nodules that may resemble calluses, but the presence of palpable gritty nodules and radiographic findings of calcification are distinguishing features.
• Gout and Pseudogout: These crystal-induced arthropathies can cause tophi (urate crystal deposits in gout) or calcium pyrophosphate deposits (pseudogout) in the skin, which can be firm and nodular, mimicking calluses, especially around joints. However, the inflammatory nature, joint involvement, and crystal analysis differentiate these conditions.
• Hypertrophic Lichen Planus: A variant of lichen planus that can present with thickened, hyperkeratotic plaques, especially on the palms and soles. The presence of violaceous papules elsewhere on the body, itching, and typical lichen planus histology help in differentiation.
• Interdigital Neuroma (Morton’s Neuroma): While not a skin lesion, interdigital neuroma, a thickening of the nerve in the interdigital space of the foot, can cause pain that patients may attribute to a callus. Palpation and Mulder’s click test can help diagnose neuroma.
• Lichen Simplex Chronicus: Results from chronic scratching or rubbing, leading to thickened, leathery skin (lichenification). While it can be hyperkeratotic, the history of itching and scratching, and the distribution, usually not confined to pressure areas, are differentiating factors.
• Palmoplantar Keratoderma: A group of inherited or acquired disorders characterized by abnormal thickening of the skin of the palms and soles. These are usually more extensive and symmetrical than typical calluses and often present from childhood.
• Keratosis Punctata of Palmar Creases: Small, punctate keratotic plugs within the palmar creases. These are usually asymptomatic and distinct from typical calluses by their location and small, pitted appearance.
• Porokeratosis Plantaris Discreta: A type of porokeratosis presenting as a solitary, well-circumscribed lesion with a thread-like border on the sole. The characteristic clinical appearance and sometimes histopathology aid in diagnosis.
• Porokeratosis Palmoplantar et Disseminata (DSAP): A more widespread form of porokeratosis that can affect palms and soles with multiple lesions. Family history and the typical clinical presentation of porokeratosis are helpful in diagnosis.

Figure: Clavus (corn) on the sole, demonstrating a well-defined focal area of hyperkeratosis, contrasting with the diffuse nature of a callus.

Diagnostic Approaches for Callus Differential Diagnosis

A thorough diagnostic approach is essential for accurate callus differential diagnosis. This typically involves:

1. History Taking: Detailed history including:

   • Onset, duration, and progression of the lesion.
   • Location(s) of the lesion(s).
   • Symptoms: pain (type, severity, aggravating factors), itching, bleeding.
   • Medical history: diabetes, peripheral neuropathy, rheumatologic conditions, skin conditions.
   • Occupation and activities: to identify potential sources of friction or pressure (e.g., automotive work, specific tools, footwear).
   • Previous treatments and their outcomes.

2. Physical Examination: Careful examination of the lesion:

   • Inspection: Assess size, shape, borders, color, surface texture, presence of skin lines, and any distinguishing features like black dots or a central core. Examine surrounding skin and other areas of the body for additional lesions.
   • Palpation: Evaluate tenderness to direct pressure and lateral pressure. Assess consistency (firm, soft, gritty).
   • Paring: Gentle paring of the lesion surface (if appropriate and by a trained professional) can reveal underlying features. Look for black dots (warts), pinpoint bleeding (warts), or a distinct core (corn). Note the presence or absence of skin lines within the lesion.

3. Dermoscopy: Dermoscopy can be a valuable non-invasive tool to differentiate calluses from plantar warts and other conditions. Dermoscopic features to assess include:

   • Vascular structures: Plantar warts often show thrombosed capillaries (black dots, red dots, or globules), while calluses typically lack these.
   • Skin lines: Calluses usually show preserved skin lines passing through the lesion, while plantar warts interrupt skin lines.
   • Homogeneous hyperkeratosis: Calluses show a more uniform hyperkeratotic pattern compared to the irregular surface of warts.

4. Radiographs: In cases of recurrent or persistent calluses, especially on the feet, radiographs may be helpful to identify underlying bony prominences or deformities that contribute to abnormal pressure distribution.

5. Biopsy and Histopathology: Rarely necessary for typical calluses or corns, but biopsy may be indicated if the diagnosis is uncertain, the lesion is atypical, rapidly growing, painful, bleeding, or unresponsive to treatment, to rule out other conditions like poroma, warty dyskeratoma, or skin cancers (though very rare in this context). Histopathology can definitively differentiate between various hyperkeratotic lesions.

6. Other Investigations: Depending on the differential diagnosis, other investigations might be considered:

   • Potassium hydroxide (KOH) preparation: To rule out fungal infections (tinea pedis) if there is associated scaling or interdigital involvement.
   • Blood tests: To evaluate for underlying conditions like gout, rheumatoid arthritis, or diabetes if clinically indicated.

Management Overview (Brief Context for Differential Diagnosis)

While the focus is differential diagnosis, briefly mentioning management provides context. Management of calluses and corns varies depending on the severity, symptoms, and underlying causes. General approaches include:

• Conservative Measures:

  • Pressure relief: Properly fitting footwear, orthotics, padding, cushions to reduce friction and pressure.
  • Regular paring: Gentle removal of excess keratin by a podiatrist or trained professional. Self-paring should be approached cautiously, especially in individuals with diabetes or neuropathy.
  • Keratolytic agents: Topical salicylic acid, urea creams to soften and thin the hyperkeratotic skin.
  • Emollients: To keep skin hydrated and prevent fissures.

• Surgical Intervention: In rare cases, surgical correction of underlying bony deformities may be considered for recurrent corns unresponsive to conservative treatment.

Important Note for Automotive Professionals: For automotive technicians and individuals in similar professions, preventive measures are crucial:

• Appropriate Footwear: Wearing well-fitting, supportive work boots can significantly reduce foot callus and corn formation.
• Gloves: Using work gloves can protect hands from friction and pressure during tool use, minimizing hand calluses.
• Regular Foot Care: Encourage regular foot hygiene, moisturizing, and professional foot care for persistent issues.

Conclusion

Accurate differential diagnosis of calluses is essential for appropriate management and patient care. While calluses themselves are typically benign responses to mechanical stress, differentiating them from conditions like plantar warts, corns, and other dermatological entities is crucial to ensure that underlying conditions are not missed and that patients receive the most effective and targeted advice. For automotive professionals and others at risk, understanding these distinctions and implementing preventive measures are key to maintaining skin health and comfort in physically demanding occupations. If there is any doubt about the nature of a skin lesion, seeking professional medical advice from a dermatologist or podiatrist is always recommended.

References

1.Takehara K, Oe M, Ohashi Y, Tsunemi Y, Kadowaki T, Sanada H. Differences Between Patient-Reported Versus Clinician-Observed Nonulcerative Signs and Symptoms of the Foot in Patients With Diabetes Mellitus. J Wound Ostomy Continence Nurs. 2019 Mar/Apr;46(2):113-116. [PubMed: 30747799]

2.Araguas Garcia C, Corbi Soler F. Effect of debridement of plantar hyperkeratoses on gait in older people – An exploratory trial. Arch Gerontol Geriatr. 2018 Sep-Oct;78:7-13. [PubMed: 29879593]

3.Rodríguez-Sanz D, Tovaruela-Carrión N, López-López D, Palomo-López P, Romero-Morales C, Navarro-Flores E, Calvo-Lobo C. Foot disorders in the elderly: A mini-review. Dis Mon. 2018 Mar;64(3):64-91. [PubMed: 28826743]

4.Singh D, Bentley G, Trevino SG. Callosities, corns, and calluses. BMJ. 1996 Jun 01;312(7043):1403-6. [PMC free article: PMC2351151] [PubMed: 8646101]

5.Farndon L, Barnes A, Littlewood K, Harle J, Beecroft C, Burnside J, Wheeler T, Morris S, Walters SJ. Clinical audit of core podiatry treatment in the NHS. J Foot Ankle Res. 2009 Mar 13;2:7. [PMC free article: PMC2663778] [PubMed: 19284645]

6.Elwell R. The management and treatment of hyperkeratosis. Br J Nurs. 2017 Apr 27;26(8):468-470. [PubMed: 28453323]

7.Bonavilla EJ. Histopathology of the heloma durum: some significant features and their implications. J Am Podiatry Assoc. 1968 Oct;58(10):423-7. [PubMed: 5681629]

8.Gijón-Noguerón G, García-Paya I, Morales-Asencio JM, Jiménez-Cebrián A, Ortega-Ávila AB, Cervera-Marín JA. Short-term effect of scalpel debridement of plantar callosities versus treatment with salicylic acid patches: The EMEDESCA randomized controlled trial. J Dermatol. 2017 Jun;44(6):706-709. [PubMed: 28012190]

9.Kovar P. [Calluses, corns and others – beware of the self-treatment!]. MMW Fortschr Med. 2016 Dec;158(21-22):64-66. [PubMed: 27966126]

10.Bae JM, Kang H, Kim HO, Park YM. Differential diagnosis of plantar wart from corn, callus and healed wart with the aid of dermoscopy. Br J Dermatol. 2009 Jan;160(1):220-2. [PubMed: 19067694]

11.Borchgrevink GE, Viset AT, Witsø E, Schei B, Foss OA. Does the use of high-heeled shoes lead to fore-foot pathology? A controlled cohort study comprising 197 women. Foot Ankle Surg. 2016 Dec;22(4):239-243. [PubMed: 27810021]

12.Phillips S, Seiverling E, Silvis M. Pressure and Friction Injuries in Primary Care. Prim Care. 2015 Dec;42(4):631-44. [PubMed: 26612376]

13.Farndon LJ, Vernon W, Walters SJ, Dixon S, Bradburn M, Concannon M, Potter J. The effectiveness of salicylic acid plasters compared with ‘usual’ scalpel debridement of corns: a randomised controlled trial. J Foot Ankle Res. 2013 Sep 24;6(1):40. [PMC free article: PMC3856524] [PubMed: 24063387]

14.MENDELSOHN SA. Arthroplasty of fifth toe for removal of heloma durum. J Natl Assoc Chirop. 1957 Feb;47(2):81-2. [PubMed: 13406525]

15.Kurtz CM, Guthrie JD. Syndactylization: a surgical approach to heloma molle. J Foot Surg. 1984 Sep-Oct;23(5):407-9. [PubMed: 6094645]

16.Stewart WP. Syndactylism in podiatric surgery. Clin Podiatr Med Surg. 1986 Jan;3(1):65-76. [PubMed: 2937524]

17.Marti-Martinez LM, Lorca-Gutierrez R, Sánchez-Pérez SP, Garcia-Campos J, Fernández Ehrling N, Ferrer-Torregrosa J. Efficacy and safety of condylectomy with minimally invasive surgery in the treatment of interdigital corns of the lesser toes compared to conservative treatment. J Foot Ankle Res. 2021 Mar 20;14(1):20. [PMC free article: PMC7981973] [PubMed: 33743792]

18.Coughlin MJ, Kennedy MP. Operative repair of fourth and fifth toe corns. Foot Ankle Int. 2003 Feb;24(2):147-57. [PubMed: 12627623]

19.Güngör S, Bahçetepe N, Topal I. Removal of corns by punch incision: a retrospective analysis of 15 patients. Indian J Dermatol Venereol Leprol. 2014 Jan-Feb;80(1):41-3. [PubMed: 24448122]