Ainhum 

Updated: May 02, 2017
Author: Jeannette Rachel Jakus, MD, MBA; Chief Editor: Dirk M Elston, MD 

Overview

Background

Ainhum (dactylolysis spontanea) is a condition of idiopathic etiology involving a bandlike constriction of the soft tissue of a digit. Generally, the constriction presents bilaterally, with involvement of the fifth digit most commonly. Pseudoainhum is a similar condition that occurs as a secondary event resulting from certain hereditary and nonhereditary diseases that lead to annular constriction of digits.

Ainhum predominantly affects black patients in tropical regions. Although it has been reported in temperate areas, ainhum appears to be increasingly less common in the United States.[1, 2]

The origin of the term ainhum is unclear. In 1867, the term was used by da Silva Lima[3] from Bahia, Brazil to report the first published case. The word ainhum means fissure in the language of the Nagos tribe of Brazil and may be related to ayun, the word for saw in the Lagos tribe of Nigeria. The synonym for ainhum is dactylolysis spontanea.

Pathophysiology

In true ainhum, dactylolysis of a toe (most commonly, but not always,[4, 5] the fifth toe) most likely is triggered by trauma; however, the true cause remains unknown. The trauma may be related to walking barefoot in the tropics. A fibrotic band develops from a flexural groove and progressively constricts the full radius of the toe until spontaneous autoamputation occurs. A similar progression occurs in pseudoainhum because of a collagen band, rather than from fibrosis. Pseudoainhum may be acquired or congenital as discussed in a father and son case that described differing types of constricting bands.[6]

Ainhum most commonly affects the feet, but in rare instances it can affect the fingers, as shown in the image below.[7]

Ainhum of the finger. Courtesy of Hon Pak, MD, and Ainhum of the finger. Courtesy of Hon Pak, MD, and reviewed by Ross Levy, MD.

Epidemiology

Frequency

United States

Approximately 130 cases have been reported in the United States, but only 30 cases have been reported since 1960. Pseudoainhum is a rare disorder.

International

The highest incidence of ainhum appears to be reported among black people of Africa, where the incidence range is 0.2-2%. The incidence of true ainhum outside of Africa appears to be low.

Race

Ainhum has been reported to affect all races but occurs most commonly in individuals of African, Asian, West Indian, North American, and Central American descent. No racial predilection exists for pseudoainhum.

Sex

In Nigeria, one study revealed an incidence of 2.48 cases per 1000 males and 1.08 cases per 1000 females; however, recent investigations suggest no sex preference.

Age

Full-blown ainhum is uncommon in persons younger than 30 years and older than 50 years. The reason ainhum appears to be age specific is unclear. Early lesions may be observed in childhood.

Prognosis

Outcome is related to the stage in ainhum when the disease is diagnosed. Pain may be severe in ainhum and in pseudoainhum. Because ainhum occurs primarily in tropical areas, secondary infections and their complications may be a source of morbidity.

Patient Education

Instructions in good foot care are critical. Since some cases of ainhum and pseudoainhum are familial, other family members may require examination.

 

Presentation

History

Criteria for diagnosis involves three conditions: soft tissue constriction, bulbous enlargement of the toes, and thinning or lysis of phalangeal bones. As the condition progresses, confirmation can be made via radiographic imaging.

The four stages of ainhum are as follows:

  • Grade I involving a groove with no swelling visible and no bone involvement

  • Grade II is a bulbous enlargement of the digit distally, resulting in external rotation

  • Grade III consists of osseous involvement

  • Grade IV is the development of autoamputation

 

Physical Examination

The clinical presentation depends on the stage to which the ainhum has progressed. The initial sign of a painful fissure under a toe may not be defining, but the progressive constriction at the base of the toe with distal edema is diagnostic of ainhum. The toe may become rotated, clawed, and dorsiflexed at the metatarsophalangeal joint. Ultimately, before the toe is shed, it may be attached by an increasingly slender thread of fibrous tissue.

The clinical, histologic, and radiographic appearances in pseudoainhum are similar or identical to true ainhum.

Causes

In 1952, Wells and Robinson[8] proposed 4 distinct sources of annular constrictions of the digits. The sources include (1) annular scarring from frostbite, burns, or trauma, (2) true ainhum, (3) constricting bands that simulate ainhum, and (4) congenital bands.

The exact etiology of true ainhum is unclear. Race and climate apparently are predisposing factors. Ainhum also may have a genetic component, since ainhum has been reported to occur within families. Infection and walking barefoot in childhood are linked to ainhum but probably are not major factors in its development. Abnormal scarring does not appear to be a cause; ainhum and keloid formation rarely occur in the same individual.

Complications

Secondary infections may complicate ainhum. If more than just the two fifth toes are affected in ainhum or pseudoainhum, the individual's balance may be affected when walking. Dermatophytosis complex may be a complication.

 

DDx

Diagnostic Considerations

Also consider the following:

Ainhum

Initial fissuring beneath toes may be mistaken for trauma or infection. Dermatophytosis complex may be a complication. In the tropics, where most true ainhum occurs, Hansen disease, syphilis, yaws, and tuberculosis must be excluded. Radiographically, osteolytic lesions may be observed both after trauma and in ainhum.

Following dactylolysis, ainhum may be confused with traumatic amputations, limb aplasia or hyperplasia, diabetic or vascular gangrene, or tourniquet syndrome (from human hair).

Pseudoainhum

Pseudoainhum[11, 12] most commonly is associated with scleroderma, Hansen disease, syringomyelia, and atypical keratoderma. Pseudoainhum refers to congenital annular bands or constrictions resulting from trauma or linked to other diseases.[13]

Congenital bands usually constrict an extremity, but may encircle any portion of the body, and result from congenital collagen dysplasia and not from scarring. The bands frequently are associated with other congenital or developmental anomalies.

Dermatologic syndromes associated with constrictive bands include amniotic band syndrome, multiple pterygium syndrome, Olmsted syndrome, popliteal pterygium syndrome, tourniquet syndrome, psoriasis,[14] discoid lupus erythematosus,[9] and Vohwinkel syndrome.[15, 16, 17]

Differential Diagnoses

 

Workup

Imaging Studies

The radiographic manifestations of ainhum are diagnostic.[18, 19]  Initially, a radiolucent band can be observed constricting the base of the involved toe, with distal swelling. Osteolysis develops in the distal and middle phalanges, with a characteristic tapering effect. Ultimately, the bone narrows until it fractures and autoamputates.

The radiographic appearances in pseudoainhum are similar or identical to true ainhum.

Histologic Findings

Histologically, ainhum shows fissuring and epidermal hyperkeratosis and parakeratosis, which is followed by a fibrotic reaction under the deepening fissure. The fibrosis is predominately composed of collagen. As scar tissue contracts, it constricts and narrows neurovascular bundles. Histologic appearances in pseudoainhum are similar or identical to those observed in true ainhum.

 

Treatment

Approach Considerations

No current treatment appears to halt the progression of ainhum.

Medical Care

Therapy for ainhum in the early stages involves topical or injectable corticosteroids, salicylate preparations, or retinoids. Pseudoainhum may respond to treatment with etretinate. Reversal of pseudoainhum with acitretin has been described in a patient with associated Vohwinkel syndrome.[20] A literature review on pseudoainhum can be found in the International Journal of Dermatology.[21]

Surgical Care

Surgical treatment for grade I and early grade II ainhum is a Z-plasty, which involves releasing the constricting base through a Z-shaped repair after surgical amputation.[22] For grade III, amputation is generally necessary. The definitive treatment for late-stage ainhum may be surgical amputation (if not autoamputation).

In the early stages of ainhum, division of the fibrous band has been reported to reduce pain.

In pseudoainhum, congenital bands rarely need treatment other than surgery.