Diagnostic Considerations

When diagnostic problems occur, they are often related to the clinician’s failure to realize that the diagnosis of ulnar neuropathy is complex and requires great care. This condition is notably harder to diagnose or localize than the more common carpal tunnel syndrome. The precise localization of an ulnar neuropathy cannot be achieved, and the clinician should acknowledge when the data are insufficient to determine where the ulnar lesion is located. Problems can occur at virtually every step.

Failure to perform a thorough history and examination (see Presentation) is probably the most crucial cause of mistakes in diagnosis. Conversely, a comprehensive history and physical examination can usually tell the clinician the most critical fact—whether an ulnar neuropathy is likely to be present—even if precise lesion localization is not always possible.

Another possible cause of misdiagnosis is failure to search for Martin-Gruber anastomosis during neurophysiologic testing (see Workup). As a consequence, the physician may inaccurately diagnose conduction block.

Similarly, failure to increase testing sensitivity by assessing nerve conduction to the first dorsal interosseous muscle and the abductor digiti minimi may cause the examiner to miss an existing ulnar neuropathy.^[109]

Another standard error is testing only one nerve in the limb, thereby missing other potential conditions, such as polyneuropathy.

Finally, the clinician may perform the electrodiagnostic tests at suboptimal limb temperatures (< 30°C), leading to falsely prolonged latencies and increased amplitudes.^[110]

In addition to the conditions listed in the differential diagnosis, other problems to be considered include the following:

Alcoholism
Burns and heterotopic bone
Diabetes mellitus
Elbow injuries and deformities
Hypothyroidism
Infections
Malnutrition
Renal disease
Perineural adhesions
Rheumatoid disease
Space-occupying lesions (including tumors)
Syringomyelia
Ulnar artery aneurysms or thrombosis at the wrist
Valgus ligament instability
Wrist fractures

Differentials

Alcohol (Ethanol) Related Neuropathy

Amyotrophic Lateral Sclerosis

Brachial Plexus Abnormalities

Cervical Disc Disease

Cervical Spondylosis

Epicondylitis

Pancoast Tumor

Thoracic Outlet Syndrome

Traumatic Peripheral Nerve Lesions

Differential Diagnoses

Workup

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Media Gallery

A schematic diagram of the elbow region with 5 main sites (as given by Posner) labeled 1-5; other sites and structures are also named. The main regions of interest are colored circles. Sites 2 and 3 are close together and cannot be distinguished by means of electromyography and nerve conduction studies. This location is referred to as ulnar (or epicondylar) groove.
The diagram shows the ulnar nerve distal to the elbow region. The dorsal ulnar cutaneous nerve (lavender) branches off the main trunk (purple). Although the course is not followed in detail after that, the lavender region on the sensory dermatome diagram shows where this sensory nerve innervates skin. Similarly, the palmar cutaneous sensory nerve (yellow) branches off to innervate the skin area depicted in yellow. The superficial terminal branch is mostly sensory (see green-colored skin on palmar surface), though it also gives off a branch to the palmaris brevis. The deep terminal branch has no corresponding skin area, because it is solely motor-innervating the muscles shown, as well as others not explicitly depicted. A nerve could be pinched or injured anywhere, but sites labeled I-IV are more commonly involved.
Inching technique used to isolate conduction block in left ulnar nerve. Note significant amplitude drop at 305 mm, which correlates with position 2 cm above medial epicondyle. This is example of supracondylar block. Image courtesy of A S Lorenzo, MD.
Normal median and ulnar patterns are compared with those of 3 commonly recognized types of Martin-Gruber anomaly.
First 3 traces correspond to ulnar compound muscle action potential (CMAP) amplitude during recording at abductor digiti quinti (ADQ) and stimulating at wrist, below elbow, and above elbow, respectively. Fourth trace corresponds to stimulation of median nerve at elbow during recording at ADQ. Although CMAP amplitude is reduced markedly above elbow, this is compensated for by adding response seen after stimulation of median nerve; this represents Martin-Gruber anastomosis.
First 3 traces correspond to stimulation of ulnar nerve during recording at first dorsal interosseous (FDI) muscle at wrist, below elbow, and above elbow, respectively. Fourth trace corresponds to stimulation of median nerve at elbow during recording at FDI muscle; this represents Martin-Gruber anastomosis.
In those with Martin-Gruber anomaly who have no other significant neuropathy or nerve compression, stimulation of specific nerves at different sites yields differing results. With the median nerve, stimulation at the elbow yields larger compound muscle action potential (CMAP) at hypothenar muscles, first dorsal interosseous (FDI) muscle, or thenar muscles (or combination thereof) than does stimulation at the wrist. With the ulnar nerve, stimulation at the wrist yields larger CMAP at hypothenar muscles, FDI muscle, or thenar muscles (or combination thereof) than does stimulation at the elbow. In this context, "larger" and "smaller" generally refer to amplitude differences ≥1.0 mV.
Riche-Cannieu anastomosis is communication between the recurrent branch of the median nerve and the deep branch of the ulnar nerve in the hand. Although it is present in 77% of hands, it yields highly variable degrees of detectable physiologic difference. In many hands, it contributes little and does not affect diagnostic findings at all. The most common effect is probably to give ulnar innervation to some muscles usually innervated by the median nerve, median innervation to muscles usually innervated by the ulnar nerve, or both. The most extreme version is the so-called all-ulnar hand (very rare). Two examples of confusion this might cause are as follows: (1) a median lesion could cause denervation in typically ulnar muscle, such as adductor digiti minimi (adductor digiti quinti) or first dorsal interosseous muscle, and (2) an ulnar lesion could cause denervation in typically median muscle, such as flexor pollicis brevis or abductor pollicis brevis.

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Table. Types of Martin-Gruber Anastomosis

Table. Types of Martin-Gruber Anastomosis

Type	Anatomy	Most Characteristic Finding	Confirmation	Additional Verification	Potential Clinical Confusion
I	Crossover fibers innervate hypothenar muscles	Ulnar stimulation at wrist* produces larger hypothenar CMAP than stimulation at elbow	Stimulation of median nerve at elbow† produces response at hypothenar muscles	Hypothenar CMAP from ulnar stimulation at wrist is equal to hypothenar CMAP from ulnar stimulation at elbow plus hypothenar CMAP from median stimulation at elbow	Smaller response from proximal stimulation could be mistaken for conduction block
II	Crossover fibers innervate FDI muscle	Ulnar stimulation at wrist produces larger FDI CMAP than stimulation at elbow	Stimulation of median nerve at elbow produces response at FDI	FDI CMAP from ulnar stimulation at wrist is equal to FDI CMAP from ulnar stimulation at elbow plus FDI CMAP from median stimulation at elbow	Usually none, because FDI muscle is not usually recording site; if it is used, conduction block could be suspected, as in type I
III	Crossover fibers innervate thenar muscles (typically ADP and FPB)	Elbow stimulation of median nerve produces greater thenar response than wrist stimulation	Ulnar stimulation produces thenar CMAP with initial positive deflection; it is higher with wrist stimulation than with elbow stimulation	For thenar CMAP amplitudes, median elbow stimulation amp is equal to median wrist stimulation amplitude plus ulnar wrist stimulation amplitude minus ulnar elbow stimulation amplitude	Can complicate median nerve studies, especially when carpal tunnel syndrome is involved
ADP—adductor pollicis; CMAP—compound motor (or muscle) action potential; FDI—first dorsal interosseous; FPB—flexor pollicis brevis. *Ulnar stimulation at the wrist yields larger CMAP at hypothenar muscles, FDI, or thenar muscles (or sometimes a combination of these) than stimulation at the elbow. †Median stimulation at the elbow yields larger CMAP at hypothenar muscles, FDI, or thenar muscles (or sometimes a combination of these) than stimulation at the wrist. Note: "Larger" and "smaller" generally mean amplitude difference ≥1.0 mV.

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Author

Elanagan Nagarajan, MD, MS Assistant Professor of Neurology, University of Tennessee College of Medicine-Chattanooga, Erlanger Health System

Elanagan Nagarajan, MD, MS is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, American Epilepsy Society, American Headache Society, Movement Disorder Society

Disclosure: Nothing to disclose.

Coauthor(s)

Sireesha Murala, MBBS Postdoctoral Research Associate, Division of Medical Genetics, Department of Pediatrics, Duke University Medical Center

Sireesha Murala, MBBS is a member of the following medical societies: Indian Medical Association, Medical Council of India

Disclosure: Nothing to disclose.

Chief Editor

Nicholas Lorenzo, MD, CPE, MHCM, FAAPL Co-Founder and Former Chief Publishing Officer, eMedicine and eMedicine Health, Founding Editor-in-Chief, eMedicine Neurology; Founder and Former Chairman and CEO, Pearlsreview; Founder and CEO/CMO, PHLT Consultants; Former Chief Medical Officer, MeMD Inc

Nicholas Lorenzo, MD, CPE, MHCM, FAAPL is a member of the following medical societies: Alpha Omega Alpha, American Academy of Neurology, American Association for Physician Leadership

Disclosure: Nothing to disclose.

Additional Contributors

Stephen A Berman, MD, PhD, MBA Professor of Neurology, University of Central Florida College of Medicine

Stephen A Berman, MD, PhD, MBA is a member of the following medical societies: Alpha Omega Alpha, American Academy of Neurology, Phi Beta Kappa

Disclosure: Nothing to disclose.

Charles F Guardia, III, MD Instructor in Neurology, Department of Neurology, Dartmouth Hitchcock Medical Center, Geisel School of Medicine at Dartmouth; Associated Neurologists, Nuvance Health

Charles F Guardia, III, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Epilepsy Society, Radiological Society of North America

Disclosure: Nothing to disclose.

Acknowledgements

Sandeep K Aggarwal, MD Clinical Assistant Professor of Neurology, Department of Neurology, Northwestern University Medical School